Throttle Position Sensor causing misfire above half throttle?

[fourbarrel]

I have had a nagging issue with my sled for years now and have been trying to sort it out myself with the help of this site and a couple other sources for information but have had no luck yet in curing my problem.First I'll start with what the sled is and it's a '98 SRX 700 with the electronics from a '00 which includes the stator,wiring harness,cdi,carbs,regulator and headlight.Basically a 2000 with a '98 engine and I used a flywheel from an '01 SXR to get around having to change the crankcase for the pickup coil location.So now onto my gremlin that's been plaguing this sled for years now.When I'm riding the sled at normal trail speeds using less than half throttle it works fine but as soon as I jam it above half it'll pull for 50 ft or so and then only run on 2 cylinders,but if I back out of the throttle it'll pick up the lost one.It has been driving me nuts.I have been through the intake side as thoroughly as I can with having cleaned the carbs multiple time,changed the reed petals to new ones on stock cages,the gas lines are oem and only a few years old and I even broke down and replaced the fuel pump with a new one 2 seasons ago.The only thing I haven't checked is the in tank line for cracks but that's still on the list.The in tank filter was removed years ago in favor of an inline one and I have a stainless weight around the line holding it on the bottom of the tank.

I have tested the tps and set it according to the service manual and it is within spec so I ruled it out but I can't help but wonder if there's a flat spot in the windings I didn't pick up with my ohm metre that might cause this issue.Other than the ignition coils as a possible source of the cylinder cutout I'm not sure where else to look or check.I ohmed out the plug caps and they were fine but I didn't measure the coils yet so that's another thing still on the list.I have the carb floats set to 14mm and they're jetted with 152.5 mains straight across and 45 pilots which I am thinking about swapping the 42.5's back in.The cylinders are trail ported which is why the bigger jets are in but the misfire has been with me before the porting work was done.
I tried searching for faulty tps symptoms but didn't get much for results so I'm hoping someone will chime in here and perhaps provide a list of symptoms to go along with some testing procedures.

 

[mod-it]

Have you tried by-passing the TORS for a test? (I doubt this is it, but why not since it's so easy to by-pass and check)
Is it always the same cylinder that drops? If so, which one? And I'd try swapping coils/wires to see if problem follows.
Harness checked for rub-throughs? (and under left footwell)
What does mid and top end jetting look like on the plugs? I believe SRX's ran one cylinder's main jet richer than the other two, but someone else will have to say which one as I'm not sure.
It would be one of my last checks, but crank in phase? I assume it got the recall work done.

These would be my starting points. I'm not familiar enough with the electronic changes between the years to know if swapping different year's parts could be the issue. I'd hit up MrViper on that one.

 

[snomofo]

Sideshow Bob did some diagnostics on his ’02 which, if I remember correctly, found the resistance output from his TPS (off idle) was sporadic - causing changes in base timing which were witnessed using a timing light.
I think his symptom was his ’02 didn’t pull like he expected and performance was inconsistent. I don’t think he was losing cylinders.

I would suggest checking resistance of the TPS while slowly moving it through its range. The resistance change should be smooth throughout and if your meter goes open or the readout jumps around while rotating the throttle, I would change the TPS.