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I just bought a 2001 Suburban 2500 2WD with the 8.1L and the 4L80e.  She came from an impound auction and the PO had the steering column hotwired and busted.  She had the check engine light on with 4 codes for the transmission.  One of them was p1860 and I forget the rest.  When driving in D she starts off fine in first gear, but holds it to about 4k rpm or until you just lightly ease off the gas.  She also hesitates just slightly engaging into reverse.  So I read that a faulty ignition switch could trigger those trans codes, so I replaced the column and put a new ignition switch in.  The check engine light is gone, but she still does the same thing holding first.  All other gears are fine and she shifts through the other gears no problem, still hesitates engaging reverse though.  I changed the trans fluid and filter, still same exact thing.  

I just bought a transmission pressure tester and will check that.  If anyone has any suggestions on what to look for I would appreciate it. 


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  • 4 weeks later...

I have thrown parts at this trans and it is still doing the same exact thing.  I got a line pressure gauge and tested it.  At idle in P, N or D it would be at 40 psi, once I gave it a little throttle it would jump up to 90.  When I drove it, it would get up to 130 +- 20.  Reverse in idle was 60, but once I gave a little throttle it would jump up to 100+.  Hard to get good reverse pulls monitoring the gauge, but it seemed reverse would go above 150 psi pretty easily while driving it.

So I figured I would replace the valve body with a remanufactured one using the transgo upgrades.  She still does the exact same thing.  Holds first until about 4k rpm and shifts hard.  All other gears shift fine, maybe a little harsh, but all at the right range. Reverse takes a couple of seconds to engage.  Absolutely no slipping at all.

Also, last night when I got home from a 30 mile drive I pulled forward to parallel park, when I put it in reverse, she stalled.  I started her back up and went backwards and parked.  She spewed tranny fluid out of the dipstick and made a mess.  I have checked the fluid when hot and had her exactly where it should be.  

Next I have ordered the speed input sensor.  The only other thing I can think of is internal issues like the pump, which I am hoping to avoid. I really don't want to rebuild this trans, but I have rebuilt a couple of 4l60e's.

Any help would be appreciated.


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