96 Rodeo 3.2 no power and sputtering until TPS is > 60%

Hi all. This problem just started on my 3.2L Auto 4X4 Rodeo a few days ago. The truck is still drivable but very annoying. Basically not much happens in the way of acceleration until the TPS goes over 60% (on my scantool) at which time the truck sounds and runs fine. As you can imagine this doesn't work very well in traffic, as it's either idling along or almost floored to make the truck go! Now the idle is not very smooth and it's definitely not running right. The only codes I got were P0440, but I cleared that one and it hasn't come back since (months). The alternator is new as well as the battery, 14.5volts driving around. The transmission seems healthy and the truck is starting out in the the proper gear. The problem at first almost seemed like the truck was stuck in 4th gear, but I've verified that it starts in 1st and shifts normally through the rest of the gears. I just tried a test a few minutes ago and tried to pull away from a stop light in 'Winter Mode'. The truck didn't have enough power to start going, made a few muffled backfiring noises, something is up. Where would you start? Thanks for any info!

Update:

Today I replaced the plugs and air filter with no improvement. The truck revs up fine in neutral but under load it still has a serious problem. An easy way to test it in the driveway is for me to put it in 'Winter Mode', hold the brake so the truck will not move and then give it some gas. It seriously struggles and will backfire (not very loud though) until the pedal goes 60% TPS. I also checked the fuel pressure. 38psi hose on, 47 psi hose off the regulator. Spark plug boots looked good, nothing fried there. Anyone?

Update:

Fuel pressure holds nicely for an hour or so after the truck is turned off so that tells me the check valve in the pump is ok and there isn't an injector stuck open.

I would love to get in contact with someone that knows what happens inside the ECM at 60% TPS. At the instant the TPS reads 60% the truck wakes up and runs out like it should. Maybe the EGR gets turned off (or on), maybe something else it turned off or opened causing proper airflow and then the truck runs like it should. Anything under 60% TPS the truck has no power, there is even one spot in the pedal where the truck will loose speed, it's that bad.

Cats plugged?

Spark leak is greatest at lower rpms. Your truck could be missing then, but clear up at higher rpms. It is odd that it happens at 60% throttle exactly, but I think it is worth pulling spark plugs and trying to find the cylinder which may be misfiring. Or disconnect the connector at each coilpack to see which coilpack, if disconnected, leads to no change in the way the engine runs. I don't know that a visual inspection of a coilpack is enough to say it is good. Mine looked fine when it died.

Use the analog setting to determine if your TPS keeps continuity before 60%, if not, low spot has formed, replace TPS