Possible Transmission, TPS or Rear Gearing Problems
 

I have a 88 Jeep XJ with a 4.5" RC lift, running 31's. It has the stock gearing in the back, and has the 4L i6 with the stock transmission. I took it in to my mechanic in plano for some major over-due maintenance that the past 5 owners didn't do. Since I've owned the jeep it had some acceleration problems. I would have to floor it to get it to start shifting. My mechanic adjusted the TPS, because he said when he got to it it was dangling inside the throttle body. He adjusted it but said that one of the 3 bolts was snapped of and would have to be drilled out.

Now I live in Collin County, not a lot of hills, but I'm constantly on the highway. I had to go to a family function this past weekend, 20 miles west of Lafayette (spelling?). On the way there the jeep would really struggle to keep the speed limit of 75 mph in the hilly parts of the highway.

I learned to drive in 2 v8 trucks, so I'm not used to having to floor it when I need a little power.

Could anyone help? I would really appreciate it.

Just thinking on my own, I've narrowed it down to 3 sources.
-the TPS is out of whack again
-the stock rear gears can't provide enough torque, or is torturing the engine
-the "good Toyota" transmission has something wrong with it

How many miles are on it?

I'd suggest getting a new throttle body and TPS, since yours can't be replaced?
No telling how long that thing's been on there.
Certainly much cheaper than tearing into the transmission or the rearend... Start with the cheapest things to fix and hope they fix it -- if not, move on to the bigger things.

Also, I might suggest a tune-up... Mine was having surging and bogging issues (would hit a certain RPM point then drop to idle, then surge back up to that point, all with the pedal held steady) and I replaced the TPS, which fixed my surging issue, but it was still bogging a bit... Replaced the cap, rotor, plugs, and wires (I got an Accel kit with copper plugs, 8mm wires, and a brass-terminal cap for like $65), and it's running like a top.

When the mech. got it the tps showed valid readings (ohms I guess). So the tps shouldn't be bad. I'll have to take the TB off and drill out the bolt.
I gave the jeep a whole tune up when I got it 1 1/2 years ago.
It has a little over 200 k miles on it

Mine didn't throw a code for the TPS, but replacing it still fixed my surging.
So just

Sorry, post got cut off. Anyway...

So just because you aren't getting a code doesn't mean it's working perfectly.

"Just thinking on my own, I've narrowed it down to 3 sources.
-the TPS is out of whack again
-the stock rear gears can't provide enough torque, or is torturing the engine
-the "good Toyota" transmission has something wrong with it"

Or, just maybe it's just a 25 year old Jeep with 200,000 miles on it, and not designed to drive @ 75 mph down the highway.

And the TPS is held on by 2 screws, not 3.

OP: Click on the pink link in my signature and do the procedures outlined in posts # 1 through 4 on your own and see what happens.

And, for proper TPS adjusting procedures, go to post #8.