Anyone experience their t-100 start burping coolant after a good hard run of 50 miles or so? No overheating, the gauge never moves past half way to hot. But 3-5 seconds after stopping & shutting off engine she starts heaving coolant in spurts. Any one have a clue what is going on?

Radiator cap?

Radiator cap is correct range.-How can I check it without paying for pressurrising the system at a radiator shop?

See if your local chain autoparts store has a cooling system pressure tester available for rent. It looks like a bicycle pump. There should be an adapter to test the cap.

Yup, common problem, Just purchase a can of stop leak and run it until you have a concern, then trade it in on a GMC.

Cap sounds right.