I have the 4L60E transmission in my 1999 Blazer. I recently finished an engine swap and got it running, only to discover that it is having issues shifting. My father and I did some troubleshooting and narrowed it down to no 1st gear or 4th gear (OD) (due to high RPM's to get it rolling forward and high RPM's at anything above 40 mph, also only one shift detected when watching RPM's) . We did the research and found that the cause was 1) Shift Solenoid A 2) A wiring harness issue (according to 30 Common 4L60E Transmission Problems & Repair | Charlotte NC - Twin Transmission). I replaced shift solenoid A and the wiring harness (wiring harness was for a different issue) and am still having shifting issues. Recently, the code P0751 showed up (Shift Solenoid A Performance/ Stuck off) Anyone came across this and fixed it before? I still have the brand new solenoid. What steps can I take to troubleshoot it? Thanks

 

Sounds like you have lost power to transmission. Does the indicator light up in all gears on the dash? Also check fuses.

 

All the indicator lights come on, however the light that tells me what gear I'm in does not. I went ahead and checked the fuses, and to the best of my understanding I was supposed to look at the Brake-Transmission Shift Interlock Fuse (under the hood fuse box). It checked out as fine. Is there a different fuse I should be looking at?

 

You are losing power. Did you have the switch on the side of trans unplugged where shifter cable attaches?

 

To the best of my knowledge nothing has been disconnected on the driver's side of the transmission (that is the right side, right?). When I crawled under there and looked, I did not find anything that looked amiss, but then again I wasn't totally sure what I was looking for.

 

This is what I was referring to.

May want to check all wiring harness in engine bay for pinched or broken wires that lead down to transmission.