1996 Chevy Tahoe hot starting

I have had this truck from new and never had any starting problems. Suddenly one day it was reluctant to start from warm. Since then the problem has worsened . It still will start instantly and run normally from cold but even after the shortest of runs with the water temperature hardly registering, it has to be churned over and over and finally will fire up very unevenly and will stall if drive is engaged. After several such sequences, the engine will fire up reluctantly and run ok till the next time I stop and try to restart. Help please
Chrispull