91 lurching and accelerating slowly

[boulders]

Hi, this is my first post, hopefully it’s in the right section.

So I have a 91 land cruiser, 205,000 miles. It has never accelerated great, getting on the freeway and such it would sloooowly reach 65 mph. I chalked this up to a quirk, not a super gutsy engine or something.
Found out the spark plugs needed replacing so we did that, but still same issue, ran the same.

It was due for an oil change as trans service so we did both and ever since then the truck is running worse. It will rev real high at 20mph and lurch, then accelerate at a snail’s pace, much worse than before. What could be going on? It sounds like the throttle position sensor but I’m worried something went wrong with the transmission during the fluid flush.
Thanks!

 

[BILT4ME]

Hi, this is my first post, hopefully it’s in the right section.

So I have a 91 land cruiser, 205,000 miles. It has never accelerated great, getting on the freeway and such it would sloooowly reach 65 mph. I chalked this up to a quirk, not a super gutsy engine or something.
Found out the spark plugs needed replacing so we did that, but still same issue, ran the same.

It was due for an oil change as trans service so we did both and ever since then the truck is running worse. It will rev real high at 20mph and lurch, then accelerate at a snail’s pace, much worse than before. What could be going on? It sounds like the throttle position sensor but I’m worried something went wrong with the transmission during the fluid flush.
Thanks!

Check your transmission fluid level!

How was the transmission "serviced"?

An oil change will not make it lurch, but an incorrect transmission service will. The transmission oil level must be checked with the engine running at idle, in drive, and the transmission warmed up. If it won't drive, then check it with it cold, fill it to the correct level, then drive it around and recheck, then correct the fluid level.

@jonheld is the expert on these and I'll let him chime in.

 

[jonheld]

Well, let's see. Your truck is 28 years old now.
How did you, "Found out the spark plugs needed replacing" and what did you replace them with?
What does a "trans service" mean? Exactly what was done?

There is a plethora of information regarding your engine and transmission available in this forum. You just need to search for it.
The 3FE engine in your truck was designed to run for a very long time with little to no maintenance on 3rd world fuel. It is essentially a fuel injected tractor motor, but it can be properly tuned and brought back to factory spec fairly easily. Please read through the thread posted below:
General 3FE Tune Up Info

 

[TWILLY]

Well, let's see. Your truck is 28 years old now.
How did you, "Found out the spark plugs needed replacing" and what did you replace them with?
What does a "trans service" mean? Exactly what was done?

There is a plethora of information regarding your engine and transmission available in this forum. You just need to search for it.
The 3FE engine in your truck was designed to run for a very long time with little to no maintenance on 3rd world fuel. It is essentially a fuel injected tractor motor, but it can be properly tuned and brought back to factory spec fairly easily. Please read through the thread posted below:
General 3FE Tune Up Info

I followed these directions and it made a world of difference. Thanks @jonheld for compiling this.

 

[boulders]

The fluid level is good. serviced I just mean fluids flushed and replaced.
The lurching and lack of acceleration wasn’t happening until after that so I’m mainly wondering what could have gone wrong during that to cause the problems.
I took it over a pass today and up a 6% grade it wouldn’t get over 30 mph