Throttle Position Sensor strange problem

Hi everyone, wondering if anyone has any suggestions..ok here it is:
I have a 1996 taco 4x4, 6 cy, factory sunroof and power antenna..when i first bought it used it threw a code (P0510 throttle position sensor malfunction) my first mistake I bought a after market replacement.. I should mention I have the actual service manual for this truck so...anyhow I threw another code same thing only this time added was system bank failure...so I read how undependable the after market ones were..

next I went to the dealership an bought a new TPS specific with my vin number. now both previous and this time when we changed the TPS (we used the manual and set it with in the guidelines of the service manual) the truck would start real nice and tight, the idle would be solid at around 1100 rpm for a few seconds before gradually coming down. had a little more pick up on acceleration as well....then it seems like a couple days before the check engine light shows up the truck becomes a little sluggish on acceleration and most importantly the idle at first start is now real sluggish and slowly works it's way up to normal rpm...then the check engine light pops up a day or so later........any ideas? yes we did check to make sure the TPS is still snug tight and did not move...checked all hoses, the usual....

i forgot to mention the truck would jerk like it was running out of fuel for a split sec on the freeway at around 60 as soon as your take your foot off the accelerator and the rpms drop to 2000 the truck would violently jerk 2 or 3 times...this was only happened with the aftermarket TPS....