So this has been going on for a little bit, but is very inconsistent as to when it happens. Basically, this only happens when cruising on the freeway at speed, but the car has the sensation of taking my foot off the gas even though it's still on there and the car slows down only to catch back up. I've been watching the RPM's but they don't seem effected when this happens. This leads me to believe that it is the clutch that is going out but for some reason part of me believes its ignition based like a coil is having problems firing. I've replaced the spark plugs with NGK Iridiums, the coils have been replaced with Split Fire coils and the coil harness with wire specialties. Maybe it's the ingiter?? maybe it's the clutch? maybe the fuel pump???

Also when it idle it feels fine, but ever so often it seems to skink just a little and shake the car...

Any ideas?

If it were your clutch, the RPM's would climb but speed wouldn't be affected. Plus when it happens, if it slips a lot, you'll smell it.

I'm thinking you have an issue with either fuel, air (your MAF sensors) or ignition.
You can also swing over to the RB forum and see if any one over there can help.

I agree with gold digger. I was having similar issues and I replaced both of my O2 and the car is doing much better. I noticed while cruising, the condition you mentioned happened and the car was loading up on fuel. It would hit about 12.5-13.2 AFR when it happened. That was at 3200 RPM 5th gear. The info for the O2 is in "my GTR buying experience " last page.

Ya, those figures seem about right. I had some issues on the way to work this morning, but after that I had a long day of driving all over the place and no issues for the rest of the day. I'm kind of wondering if it's something to do with the ambient temp. Either way I'll probably do a clean on the MAF's this weekend, then consider getting some new O2 sensors. Which ones did you get or which other Nissan uses the same O2 sensors?

One other thing that I just remembered. My 33-R had this thing where if I didn't let it run and warm up for a few minutes, it would hesitate if you tried to give it a bit of gas. If it was fully warmed up, it would run perfectly, but if not, it was very similar to what you're describing.

I don't think that's it because the car is usually warm when I have the issues

I used stock Nissan ones from frsports.com

So now I've dropped a new alternator in the car and changed out the up stream O2 sensor, still have the same problem, it's only when cruising over 100 kph... I don't know why but it kind of feel like fuel cut

I found this on another forum. "In my case the Crank Angle Sensor was stuffed, which caused misfiring and lack of power from 4000 rpm onwards." That and MAF has come up a lot for what you are talking about. Hope it helps

Already cleaned the mafs will try the crank sensor, I'll have to try and find out how to test it

Ok so now I've re-sodered the MAF's and replaced the igniter and am having the same issue. Anyone have any other ideas? To reiterate, the car runs fine when in traffic or cruising under 100kph. Over 100 kph the car will momentarily feel like I take my foot off the gas then will catch back up. It idles fin for the most part but ever so often the idle will sink down a little and the car will shake a little. Things fixed or tried so far:

New Splitfire Coils
New Wire Specialties ignition harness
New NGK Iridium plugs
Use igniter
New Nissan O2 Sensors
Cleaned and Resodered the MAF's
New Alternator, the pervious one died on me real fast

Just ordered a Walbro 255lph pump 5 min ago

Any ideas on what is going on here. When I first bought the car it ran fine, I've put about 10k on is since buying it and this is a problem that's been going on for about a month now.

As an up date the Walbro doesn't exactly fit to well without a lot of modification so I returned it and Ordered up a Tomei pump. As soon as I dropped it on the hesitation problem went away. Got even better when I did the rewire of the fuel pump as well. Also I believe I'm actually getting more power out of the car. It's been in a for w few weeks now so I'm confident that particual problem wont be coming back

That's good to hear. Strange how you would be starving for fuel only above 100 kph. How are the hoses going to your pressure regulator? Maybe the old pump just wasn't putting out enough volume, or the pressure reg is going. Something to think about too.

Ya, it started doing it again on Friday. I was stopping putting octane booster in the the tank. I put some in and it got better, now it only does it for the first 15 min on the freeway, but the problem is not fixed. I've also noticed a reversion back to the less powerful engine

Sounds like you need to find a new station.
Whatever crud that was in your tank maybe now in your line, so maybe try another fuel filter.
Look up Archoil 6200, as opposed to octane booster.
How is your voltage, especially you did some rewire? When a fuel pump is not performing, it's not always the pump itself and could be the voltage going to the pump.

Since I've been running the Lucas Octane booster I haven't had the issue again. I've been to numerous gas stations and this seems to be a consistent thing. I'm guessing I just ended up with one of the GT-R's that hate 91 octane piss water that California calls gas