2000 Pontiac Bonneville grounding issue?

When the weather is hot, I loose the instrument gauges, radio and power windows. AC also goes off but the blower stays on. I also lose remote entry. The car will run in this conditon but wont restart. It will all revert to normal operation when it cools down. I have changed battery and cleaned connections. I found the ground iunder the back seat and engine compartment are there others? I would take it in but it wouldn't do it at their shop.