I’m new to this forum and this would be my first post. I would usually be posting to muscle car forums as I’m usually needing some insight on issues involving my 67 Cougar, please don’t hold that against me. Looking for input from you expert and experienced Titan folks.
The scenario; two years ago I helped my boy purchase a 2006 Titan with 135k. It appeared to have been taken care of. I even called the local dealer who had the maintenance record on the vehicle and said the owners had been following the recommend maintenance schedule since they bought it new and the vehicle had no major work done at the dealership.
When we got it I did a DIY change on all the fluids including the transmission filter and fluid. I did just the pan drain not a full flush.
Now forward to last week. My boy calls me and said he heard a clunk from the tranny, then the vehicle seemed to lose power and was running sluggish.
I had him bring it by the house. Since he now had 170k on the vehicle I decided to do another transmission fluid and filter change.
When I dropped the pan and cleaned the magnets there didn’t seem to be any excessive material on them.
Something my boy didn’t tell me but I had notice, the “Service engine” light was on and the “AT check” light flashes up to 13 times when the truck is first turned on.
I took it over to a local transmission shop where I’m acquainted with the folks. They scanned for error code.
The code sheet they showed me had the following
P0744 UNDOC CODE
P1754 ICSOL VLV CKT FLT
P1757 FB SOL CKT FLT
P1759 FB SOL VLV CKT FLT
P1754 DIRECT CLUTHC SOL VLV/CKT FLT.

They informed me they’ve only seen these codes and symptom on these trucks when water has contaminated the transmission fluid. I haven’t seen any evidence of water in the fluid at any time when I’ve changed the fluids.

All this said there telling me it looks like the transmission needs a rebuild at about $3800.
I have no doubt this is well worth the money but when you aint got the money it really doesn’t matter.
I know the rebuild covers anything that could be wrong and I can appreciate the mentality of fix any possible issue that might be causing the problem so the proeblem gets fixed. BUT
I’m wondering could those codes be caused valve body and would a replaced valve body fix it?
Also how hard is it to remove and replace this transmission?
I was also wondering about buying a used transmission from junk yard and putting it in.
Any input would be greatly appreciated? .

Welcome.
All those codes make me think of poor connections in the AT harness.
Water can do things like that.
Titans don't seem to have a problem with water contamination from the radiator cooler as much as the Xterras and Frontiers do, but its possible, and needs to be fixed if its leaking. At your mileage I would consider replacing the rad even if the cooler is not leaking.
There are harder transmissions to take out than these, is it a 4WD?

Negative on the four wheel drive. It's two wheel, column shift , no locking axles or differnetial. On the wiring harness topic, I noticed the maunal shift option on the end of the column shift lever, that I never knew was there, doesnt work either. I pulled the shrowed off the steering column and found the black wire was broken. Rad fluid does look good but we'll take your advice if we can get this tranny issue resolved cheap.

Also, any direction on where or which AT connection might fail ? I put it that way becasue there are wires coming out of areas I never knew a wire could fit.

The broken wire for the manual shift switch is common, and unrelated to your main problem.
On some earlier Titans there were issues with rain/wash water getting into the AT harness and/or connector down at the trans itself. The connector points up.
It would be worth taking a look. A long flat bladed screwdriver helps get the connector off to take a look.

You know I have to apologize for something. I’ve spit off that I’m not seeing water contamination in the transmission fluid.
I’m basing my comment on what I would think would be obvious indicators of water in the fluid. That being the separation of the coolant from the transmission fluid after sitting for a little bit. I’m only assuming this would occur, I have no experience diagnosing water/coolant in transmission fluid.
I have had my fair share of experiences with water in engine oil. I was kind of going off that, which may be incorrect.

Let me ask, what would be obvious visual evidence of coolant in the transmission fluid? .

You cant always see it on the stick well.
When you drain the fluid, the stream has a distinct pale, pink, pastel look.
That's when I see it best.
I have left small bottles of it to settle and it doesn't really seem to.
Are you seeing something that has you wondering?

If I unplug the transmission wire to the vavle body what will happen?
Is there any way to by pass TCM or comptuer, which ever one is throwing the transmission code? If I can stop what ever signal from getting to what ever components that is making it go into limp mode it will help with the trouble shooting. .

Water makes oil frothy...lots of bubbles on the dipstic, or in the fluid you've drained?

I've seen several of these trucks go past that mileage, but still, 170k isn't bad on a first transmission.

It's never a convienant time for a transmission to go out but this has got to be the worst time for the cost of a rebuild. Im trying to figure the Duct tape and Chicken wire solution .

if it was me i would do the oil change (pink and not able to see through it is water pink and looks see through its ok) then i would unplug and replug all of the connections a few times (giving a spray with WD40 or similar) and then take it for a drive and see if there is any change (error codes may need to be cleared first tho)

as for doing a box swap its a little bit of an effort but since your not 4X4 that makes it so much simpler just look around the junk yards for one at a good price(try to find one still in the truck so you can see how meny K's it has on it)