agconsultor

This is my first post here, and im looking for advice from the gurus!

Hey guys, on monday i bought a 99 suburban 4wd from a friend of mines father in law. It has 102K on it, and is in great mechanical shape relatively speaking. I thought the fuel filter was the culprit, but after driving it a while i realize ive got a trans problem. I grew up with my father having a shop so im mechanically enclined slightly!

So what its doing:

Put truck in D and accelerate normally, the transmission will shift from 1-2-3-4 before the truck is going 10 mph. It lugs it down and wont kick down into lower gears. Get on it a little bit and it does shift ok, but still very quick.

Manually shift the gears from 1-2-3-4 it shifts good but really firm, moreso than my 06 that i had a shift kit in.

Highway speeds, runs fine but wont kick down into 2nd for the passing gear, only 3rd no matter what speed.

The kicker:

I drove it 70 miles this morning and didnt have any issue at all, shifted beautifully through all the gears but a little quicker than i would expect...regular accel maybe 1-2 at 1500 2-3 at 2000. Still wouldnt kick down into 2nd to pass. Parked it left it running talked to a buddy put it in drive, all the same crap as above..now it seems like converter is locking and unlocking going down the road maybe a 1-200 rpm jitter.

Its a 4wd with push button shifting, it threw a code P1875 for the 4wd low. Cleared the code...didnt change anything. Check engine light came on yesterday while the trans was shifting fine and then it turned off. Im really leaning on this possibly being computer related? Is there any help you guys can offer me?

Also i completely went in and did a filter and fluid service on the transmission...oil didnt look too bad or smell burnt.

The truck sat in a garage, and had about 300-600 miles put on it in the last 2 years.

I really appreciate it!

Mike