95 Rodeo Tranny woes??? Maybe

[USMC1341]

OKay, here's the history.....I swapped a bad alternator for one from a junkyard off of a 93 Rodeo. I was backing out of a parking place facing downhill in the snow. It wouldn't go so I threw it in 4WD and rolled forward what I thought was enough to get it locked in. Then, I tried backing up and heard a loud CLUNK!!! so I took it out of 4WD and tried backing out again. It went, so I left and down the road, it starts bucking going uphill-the engine wouldn't rev up; it just kinda felt like slippage. I gave it gas and it would get up to about 2000 RPMs and then it would "buck", the engine RPMs would drop and then it would "catch" again and the engine RPM's would go back to normal driving range-all this in the span of a second or so.

It STILL DOES THIS!!!!!! Only now, it doesn't always happen. It's like you can stand on the gas, and it will surge and stall, if that makes any sense. Think of it like having a manual tranny and leaving it in 1st gear, winding it out, then letting off the gas. The vehicle will "buck" as you let off the gas. It's only sort of like that.

It is an auto tranny; I don't know which type (I think there are a couple to choose from). These are the current stats on it:

I think I slightly overfilled the fluid in it-I didn't completely seat the dipstick when I checked it, so I inadvertently gave myself a fals fluid level reading. So I'm about 1/4 inch over the full mark on the properly seated dipstick.

I replaced the thermostat last year, and now, as it sits at idle, if I don't get rolling within a couple minutes the temperature is flying to just shy of the redline. I checked the fan clutch in the following manner: I taped one of the fan blades to the plastic shroud with SCOTCH TAPE and let it run to almost redline. The fan clutch never kicked on, and after removing the tape, I could still stop the fan with my hand.

I'm running up over 138K miles on an original timing belt, and a set of plugs/wires that are old as all hell. I guess I need to make time for it, huh???

When I experience the "bucking", if I am at highway speed, I have put it in neutral, shut the ignition off momentarily, and then restarted the engine. When I put it back in gear, it has worked fine SOMETIMES and sometimes it only alleviates the problem to an extent.

I have read a few posts on here about range/mode sensors being bad, a couple about fan clutches, and a couple about the alternators affecting the tranny. I have no clue and before I dump a wad of cash to some damned shop, if it's something I can tinker with given a limited set of tools, I would rather do that.

DOES ANYONE HAVE ANY CLUE WHAT'S WRONG WITH THIS THING???