speedometer loses speed

What is your question?

after stopping, the speed will be normal, but after 15 min or more the speed on the speedometer will start slowing down until it will show 0 speed when we are staying with the moving traffic. stop such as getting gas and it will be normal, for a while then start up again

What makes this problem better or worse?

after starting the engine up after a short rest

How long has your 2005 Toyota Tundra had this problem?

it started on our trip back from Ga. pulling a camper