I have a 99 RAM 1500 quad cab (currently having the waterpump and all accessories replaced) that has a quirky fuel gauge issue.

Occassionally, when starting the truck, the fuel gauge doesn't budge. Usually occurs after filling the tank a day or two previous and is always when tank is fairly full. Restarting the truck once or twice typically resolves the problems. I have also actually kicked the tank to get it to register. Most likely a float issue???

Probably.

check the conections as well... the ones on top of the tank that hook up to the sender.