I have a 2000 3.9l 2wd (transmission code in glove compartment tag reads "DGB" & "DGK"). I have had no trans problems at all until the other day when suddenly it wasn't upshifting as I accelerated. Eng would rev to about 2500 then a hard shift up would occur. I found that adding a little tap on the gas followed by quickly pulling my foot off the pedal helped it pushing. Fluid level was ok. Truck sat for about 1/2 hour then drove home fine. I ordered a TPS and used the truck about 3 times while waiting. 1 time was fine, other 2 same problem. I just got the TPS,installed it took a quick test drive, no improvement! I plan to change fluid and filter next, any other things I should change while pan is off? I'm also going to check and adjust the cable from the Throttle Body. I checked and had no diagnostic codes while parked. Do I have to drive it while hooked up to the reader? Thank You in advance. Steve.