Relaced Tranny now have another problem

First of all new to the forum and hello to all.
94 Passport with V.6 4x4, 4L30E Automatic Transmission
Just replaced a very worn out and busted Tranny at 140K.
Installed a "used" Tranny and everything went smooth.
New tranny installed nice everything hooked up as planned and truck ran great for the first 30 miles or so.
The next day I took the truck out and after approx 20 miles of driving the "Check Trans" light was flashing and it went into "back up" mode.
Fluid levels are where they should be and everything "appears" to be fine!

Any suggestions?

p.s. Haven't had the codes read yet, that is the first thing on my list monday AM

Thanks in advance
Scorwell

Could be a range/mode sensor issue. Check to see if your "PRND321" lights on the dash, correspond with the gear you have selected with the floor shifter. If they dont line up (at any time), your 4L30E will go into limp mode. Other than that, you're really at the mercy of whatever the codes say.
G/luck!
Joel

got the diagnostics back from the shop and it turns out to be the 2-3 shift solenoid. HOPEFULLY

Ok got it back from the Tranny shop today, the 2-3 Shift solenoid if fact was bad, but that did not fix the problem. Transmission tech told me could have fried the computer!!!!

sounds like you got a bad used tranny. Take it back and get another one.