Chevy & GMC Vans

A few weeks ago I had an issue with starting. The engine would hesitate a moment before coming up to normal idle RPM. Around the same time, it started misbehaving in other ways. Engine had reduced power. Accelerated very slowly, especially up hills. Felt like I was taking off in 2nd gear. Transmission indicator light went out, cruise control disabled, and some other things. DIC flashed messages about air bags, traction control and stabilitrak. When I release the brake, I hear a click somewhere inside the instrument panel. System voltage with the engine running is normal.

I assumed it was a bad battery, but I didn't have time to deal with it. In the meantime, temperatures rose, and now the van starts perfectly every morning. But the reduced power + DIC messages persist. Finally today, I went to a battery dealer. He tested my battery and it was in great shape (ACDelco Professional Gold, ~3 yrs old). So now I'm stumped.

I read that the DIC messages were a common problem for GM pickups, caused by a faulty ground on the frame wiring harness, directly below the driver. When I got home I sanded the ground mating surfaces clean and reconnected, but no change. Has anyone else experienced this issue?

2013 Savana 5.3L

mechanic ran a diagnostic scan. Transmission control module isn't responding.

Can you fix that yourself? What's involved?

I just tried probing the wires at the TCM. It has good power, ground, ignition, and wake-up signal. It has 2.5V on the data network lines too. That's all I can think of. My only conclusion is that the TCM is fried. If that is the case, then it'll have to be replaced and programmed. Programming usually requires sophisticated equipment which I definitely don't have.

I have an appointment at an auto electrical shop who specializes in these things on Wed, so hopefully they can fix it for me.

auto electrical shop confirmed my diagnosis: fried TCM.
Module was replaced and programmed. Problem resolved. $670