First off i know very little about cars. i dont know proper names and wat not. recently my heater core went out so a friend and i replaced it. we didnt have time to put together the dash so i did it myself a couple of days later. now there are issues of course haha. it is very slow to accelerate in complete stops. also my speedometer and my rpms arent working. blinkers brites and emergencies work. i also have the service engine soon lite on. my car is automatic but if i put it in 2nd gear it accelerates just fine. ive read another thread mentioning wiring issues near the fuse box or just on the driver side in general. was looking for more opinions. i appreciate any input. ive put more than 20 hours into this project and its driving me crazy.

i would start with the dash pod. see if the pins on the connector are bad, i dont know your car specifically but if the vss signal goes through the speedo and then to the pcm that could be your problem. you may have disturbed or not put back a ground for the pod. but to me it seems like the connection between the pod and the wires could cause these issues

First, looks like you are new to the forum, welcome.

In addition to looking into what JW Firebird suggested (he is super knowledgeable), you might want to isolate the problems a bit more. You may have more than one problem.

I would do a scan and see what the service engine soon light was indicating. That may give another avenue to troubleshoot.

Keep us in the loop on how you you are doing with this. There are some knowledgeable people here on the Jimmy/Blazer/Bravada.

Check ALL of your fuses. It sounds like you have no voltage going to the transmission, among other things.