Ok, this is a common issue. There is a pack of grounds in the drives side floor, under the carpet. You need to pull up the trim strip that runs on the door sil and pull back the carpet. There is a black connector there with a cover. If you pop the cover off there is a piece of metal that connects about 5 or 6 spade lugs together, pull the metal strip out and clean the green crap off it with a wire wheel. Put it all back together and your problem will be gone for a while. I have seen this in several 95-2000 GM full size vehicles. It is a really stupid setup. The grounds for most items in the car run through this connector. The fuel pump ground is in there. It will usually happen after turning on a high load item like the lights or rear window defroster. Usually when the car wont start the power windows will also be real slow or wont work at all. We have actually eliminated the connector all together buy cutting off the connector and soldering all the wires together.
Hope this is your issue as it is a cheap and easy fix!!
The first one of these we fixed had been to the dealer 3 times and they couldnt find it.
Artificial Intelligence is no match for Natural Stupidity