On our 1996 gmc jimmy I replaced the transmission now it will not shift at all. did I miss something?

On the 1995 Jimmy, the shift cable can come loose on the mount on the side of the transmission where the cable meets the trans. When it slips, the alignment goes off and causes the driver to not be able to put the trans into park. If you take a long stick you can push the shift arm on the trans to the park position and your trans will go into park.....what you (and I) really need to know is how to take the shift cable mount apart and reset it.

The The Park/Neutral Position and Backup Lamp Switch is located on the left side of the transmission under the lever where the shift cable hooks up. (See picture)

Maybe my data is not up to date, but my list does not show any of these trouble codes.

This then could be a malfunction of the Computer system, have it checked out by someone that understands more then just reading a code shown on the meter....

Look for vacuum leaks. There are tons of hoses, replace dried and cracked ones....

The trans shift issue that you describe seems that the trans is being told to hold back the shift, there is a unit at the end of the vacuum tube, AT the trans, called a modulator. They have a rubber diaphram inside that fails and then trans fluid gets sucked into the engine, via this vac. hose. Pull it off and see if any trans fluid comes out...Should be ZERO.

Also, your vehicle must have regular trans service, especially you must change the FILTER. Disk material eventually clogs the filter, then trans fails really fast.

You may consider having a quick lube shop do the trans service, they use a machine that pumps new fluid in while unit is running, totally flushing converter, cooler,and lines...but DO replace the filter.

To be fair, the service suggestion has nothing to do with yoru complaint, necessarily...

IF the abs dash light is on and if the speedometer is sluggish or not working at all, it is probably a bad speed sensor on the transmission. and easy fix under $40 for the part. Mine was stuck in second gear for a while then worked then it stuck in first gear and i had the CHECK ENGINE light on.

4th gear failure is a common problem with this transmission, assuming it is an automatic. You should have the vehicle checked for codes by a qualified repair center with the proper scan tool. Also, check fluid level and condition. More often than not, the trans loses 3rd and 4th gear, as these are working off the same set of clutches. 3-4 clutches apply in 3rd, and when the 4th shift is made the 2-4 band applies giving you overdrive. If you have no engine braking in manual 3rd, you definitely have a mechanical failure, no 4th could be an electrical, or mechanical fault.

a manual transmission don't have park i am assuming you have a automatic trans in vehicle and maybe the park interlock is not working properly check fuses 1st

Inside trans. pan at the rear of the valve body. They have a wire clip which holds them in.

i had to put a new trans in my 2000 jimmy about a year ago there is something inside called a "reverse hub" its made from aluminum and not very hard to break..when mine broke i was stuck trying to move in reverse and it heard a pop then a winding down noise and sure enough its the reverse hub to fix it i just had the trans rebuilt