About two months ago, I replaced a leaky heater control valve, and shortly after, one of the plastic fittings over the valve cover disintegrated and shat out all the coolant, nearly overheating it. Recently, I got around to fixing the overheating but when I went to take it for a drive, the transmission wouldn't shift out of (second? I think? Maybe first?) gear, and after sustained medium revs, the check engine light came on. I shut off the truck and went to restart it thinking that might clear the code and/or fix the problem, but it wouldn't restart. After about 5 minutes, I tried to start it again and it fired right up with no CEL, but the exact same thing happened. Luckily, I was only about a mile from my house and when I got back home, I shut it down and, again, it wouldn't restart. It did shortly after. The truck is a bone stock, one-owner, 120k-mile Cherokee with crystal clear trans fluid and it's never given me any indication of transmission failure, so what am I looking at here? Is it a throttle position sensor? Shift solenoids? Any advice is appreciated. Thank you in advance!

 

On the passenger's side, at the back of the engine right by the firewall, there are 3 connectors that go down towards the transmission. Disassemble and clean them well with CRC QD Electronic Cleaner.