Electrical failure?

I have a 2000 Yukon Denali. Recently, while I was driving 30 mph at operating temp the engine died. Before we coasted to a stop I was able to restart and it ran normally. When I stopped I noticed that the clock had reset and the radio was now off. This has now occured several times. On several occasions, when I turn on the ignition all I get is a clicking noise around my feet. Sounds like a relay. Problem only lasts a few seconds. I've racked my brain to figure what might cause a complete (even the clock) electrical failure but can't come up with anything. Battery posts are clean. Could there be an electrical interuption caused by the stock passive security system? My regular mechanic has given up without trying since it only happens about once a week. Any thoughts would be appreciated.

I have a 2000 Yukon Denali. Recently, while I was driving 30 mph at operating temp the engine died. Before we coasted to a stop I was able to restart and it ran normally. When I stopped I noticed that the clock had reset and the radio was now off. This has now occured several times. On several occasions, when I turn on the ignition all I get is a clicking noise around my feet. Sounds like a relay. Problem only lasts a few seconds. I've racked my brain to figure what might cause a complete (even the clock) electrical failure but can't come up with anything. Battery posts are clean. Could there be an electrical interuption caused by the stock passive security system? My regular mechanic has given up without trying since it only happens about once a week. Any thoughts would be appreciated.

Might try replacing the battery cables. Posts may be clean but if the cable is bad...might short when it's hot