Hey yall,
I hope I am not violating any cardinal re-posting rules but I searched for a while before deciding to start a new thread since I can't find anything on what I am looking for. Any help would be appreciated with the following problem.

First off, let me clarify that I am in no way knowledgeable on any measurable scale in regards to transmissions, but I am not the guy building it, so it shouldn't be too much of a hindrance. My cousin is extremely knowledgeable with all things mechanical but not so much technological - hence my searching online for help. He has built a few transmissions for me (i am rough on my stuff) with no problems in the past. He has a 1,000 Hp Mud Truck he built from the ground up, literally, and has not had a lick of trouble from his transmission in over 5 years or so of running it now. Point is, I have faith in his ability. Please don't exert extra energy trying to "dumb it down" for me, I will read word for word to him and let him decipher it.

I own a 2004 Z71 Chevrolet Tahoe, with the 5.3 flex fuel (do not believe this has any bearing whatsoever, but wanted to include it just in case) and the transmission went out back in August. My cousin has now pulled it for the fifth or sixth time and still cannot get it to function properly.

The transmission was completely rebuilt with new parts (including new valve body, pump, torque converter, wiring harness, shift solenoids, all internals, etc.) and a used case (not mine because of mine being in poor condition).

The problem he is having no luck in solving is when the shift selector on the column is shifted to Drive, the truck is wanting to start in 4th gear from a dead stop. The computer is sending signal to the transmission to be in first, the transmission is reading the signal and telling his diagnostic machine that it is in first gear, but when he ran a pressure tap, it in fact was in 4th. If the column is shifted to 3rd, the computer and transmission once again are communicating electronically to start in first, but a pressure tap reveals it is in 3rd. Same thing for 2nd.

If he starts the truck in 1, it in fact is in first gear. It can be manually shifted to 2nd, 3rd, and then into 4th but will not automatically downshift if he decelerates. If it is manually downshifted, then it will downshift. (Basically, I have a manual transmission right now without the clutch pedal)

The electronics are not throwing any errors, and he has tried a few different things, including new wiring harness and two new valve bodies already as most of his contacts have suggested this may be the cause but that hasn't worked out.

Anyone have any ideas? Any help would be GREATLY APPRECIATED.


Thank you

I would check the plugs to the shift solenoids and make sure their connected properly. The colors should be color coordinated for the wires to the plugs.
Then if this is correct I would check the voltage to the plug and make sure the proper solenoid is getting power.

In addition to verifying the solenoid connections, check the wiring at the main electrical connector on the right side. There may be a difference.

You might want to check the valve body parts (again) even though the valve body has been changed multiple times. There were several variations of valve bodies, separator plates, mainshafts, pump housings, and servos over the years, so make sure the correct servos are on the correct mainshaft, and that the mainshaft is correct for the pump housing. The possibility of an incorrect shaft/pump/servo is less likely since it does apparently operate in manual mode, but the valve body, separator plate, and case must also match. Since the case was replaced, it is suspect. The numbers on the case should reveal the date, and the marking on the valve body should reveal the series. One small change there can make all the difference.

I am going to pass this along to my cousin and see what he says. I will let yall know what we find out, but not sure how long that is going to be. At the rate we have been moving, I am scared to ponder the thought.

Thanks for the information, I sincerely appreciate it!!

Ended up being a bad ignition switch causing the transmission to get low voltage. sorry i didnt post a reply sooner, but i guess its better late than never. thanks for the help!