91 R2500 Suburban 4x4 4L80E hard shift/up down shift in 2nd/3rd

[BRFoster77]

I've got a 91 suburban 3/4 ton 4x4 with a 4L80E trans that just in the last 3 days has started shifting in n out of 2nd/3rd. Does it a couple times then drops into od fine. I've never had an electronic trans, always 350, so I'm not sure where to start looking. It's shifted hard, to me, since I've had it, but dunno if that's normal or not. It is sitting on 35 inch ties with 6 inch lift as well, dunno if that's an issue or not. Thanks in advance for the help.

 

[Will L.]

Welcome. More truck info can help.
Not knowing what engine you have, possibly bad tps or out of adjustment, loose grounds, bad connections, etc.

 

[BRFoster77]

It's a tbi 350. I actually found out after posting the original question, that the trans is out of a 98 truck, and it's in a 91. From what I've read in other posts, there's issues with pressures and or controllers when late models are used in early model trucks?

 

[MrMarty51]

welcome to the forum BRF.
You might be needing a stand alone transmission controller but I know not too much about transmixers so I`ll just watch and see where this goes.

 

[THEFERMANATOR]

A 98 4x4 will not work in a 91 4x4 unless you open it up, add in an output reluctor, and a 91-93 valve body. 91-93 were there own generation of 4l80e.

 

[Will L.]

A 98 4x4 will not work in a 91 4x4 unless you open it up, add in an output reluctor, and a 91-93 valve body. 91-93 were there own generation of 4l80e.

Not to sidetrack his post, but i wonder if there is id numbers on the trans to say which is which like engine julian codes.
The reasons I ask are if one is already out of a rig.
Or hummers vs trucks- 93 last year db2 but hummer is 95
No ecm till then but a tcm.

And the 93 truck hvac controls is the hummers to 95. The 2 years behind seemed to be like that for most. Cant remember what year spin on waterpump was at the moment of each.

Anyways- there is supplies of good takeouts from civilian hummers because of guys swapping in dmax/ Allison.
Also hmmwv takeouts. Hmmwvs would get rebuilt to go back in service based on time or units- not just if they had a problem or not. Problems are swapped and left partially disassembled from diagnosis usually on engine, trans, etc. but good takeouts are normally left intact.

Also- @THEFERMANATOR idk if it is already in the stickeys or not, but if you get the chance to do a what swaps and what parts need list- that would be awesome.
Also maybe a good/ better/ best list of what upgrades to do to a trans. Major undertaking I’m sure - but just thinkin if you get really bored some weekend...

 

[THEFERMANATOR]

Not to sidetrack his post, but i wonder if there is id numbers on the trans to say which is which like engine julian codes.
The reasons I ask are if one is already out of a rig.
Or hummers vs trucks- 93 last year db2 but hummer is 95
No ecm till then but a tcm.

And the 93 truck hvac controls is the hummers to 95. The 2 years behind seemed to be like that for most. Cant remember what year spin on waterpump was at the moment of each.

Anyways- there is supplies of good takeouts from civilian hummers because of guys swapping in dmax/ Allison.
Also hmmwv takeouts. Hmmwvs would get rebuilt to go back in service based on time or units- not just if they had a problem or not. Problems are swapped and left partially disassembled from diagnosis usually on engine, trans, etc. but good takeouts are normally left intact.

Also- @THEFERMANATOR idk if it is already in the stickeys or not, but if you get the chance to do a what swaps and what parts need list- that would be awesome.
Also maybe a good/ better/ best list of what upgrades to do to a trans. Major undertaking I’m sure - but just thinkin if you get really bored some weekend...

Bored happens alot, but getting enough time to sit down and type all that out is scarce. For the 91-93 4x4, you can pull out the rear output speed sensor, and look in for the reluctor wheel. I'm pretty sure the change was across the board from 93 to 94 on the trans change. The spin on water pump was mid year 99 and I believe it was for all as well. There are some ID numbers on the trans, but there's not alot of info out there to breakdown the 3 digit codes GM stamped on the metal tag, and the paper tag is missing from many after all these years. And visual identification on 96 and earlier can be TRICKY to put it lightly with all the variations GM used of shifters.