I have a single handle shower tub control with a tub outlet diverter. When run the tub the water comes out great at whatever temp I desire. When I pull up on the tub outlet diverter to make the shower work, the water comes out cold even if I set the tub temp to hot. I've called a couple of manufactures with no solution from them. I don't know the manufacturer.

WE need the brand name of your tub/shower valve.

When I pull up on the tub outlet diverter to make the shower work, the water comes out cold even if I set the tub temp to hot Are you saying that as the water runs hot out of the spout when you pull up on the spout diverter it then runs cold no matter how hot the temp setting?
It won't run hot after you let it run for a while? I'm just attempting to understand your problem a little better. Can you furnish more details? Back to you, Tom