89 Pathfinder NO REAL POWER

[BG60]

Hello All: Sad to say I need to give you some history:
I have an 89 Pathfinder, I bought said pathfinder a few years ago with just a little over 100K. It had a blown motor from what appeared to be off road mudding that caked the raditor. The vechicle obvioulsy overheated to the point of throwing a rod out of the block. I found a replacement engine that was said to have only 70K, after taking off the oil pan I must say it might of even had less miles than told. What I did not notice about the engine and didn't think it to be a problem was the front timing belt drive assemble, including the lack of a harmonic balancer.
Turns out, it must be a late model Vg motor as the crank nose is larger. Being that I had already set the engine including front pumpkin and exhaust I went searching for a different belt drive assembly. I used a serpintene style harmonic off a Quest along with the brackets for the power steering, alt and air compressor. I of course had to modify the high pressure hose assembly that houses the power steering high pressure switch.

Everything now works and I really like the vechicle EXCEPT...the problem is NO POWER in the lower RPM band. When it makes power it is in the upper rpm's and is almost acceptable but not quite. It doesn't take much of a hill to slow down to 30 mph. I have to wonder if my parts are so mismatched that it doesn't stand a chance. If I need to change out cam shafts? Maybe I should put a 90-95 fuel injection, harness and ecm? Last tid bit...I do have the bigger tires which I know is part of the power problem. They are what I believe 31.50 15's or the equal 245x70x15.
Thank you for taking the time to help me out here!
Brian
BG60

[NismoPick]

It had a blown motor

What was the orig motor?

Turns out, it must be a late model Vg motor as the crank nose is larger.

VG30E or VG30DE ?

If I need to change out cam shafts? Maybe I should put a 90-95 fuel injection, harness and ecm?

If it's a VG30E, the adapting VG30DE fuel injection would likely be a nightmare.

What is the timing currently set to on your engine? Have you tried pulling the ecu diagnostic codes?