Ron-
     
     Just my logical mind working here, but it sounds like a delivery 
     problem to the burner (or an unlikely two bad control valves in a 
     row).
     
     When you say you replaced the thermostat, I assume you're talking 
     about the device connected to the knob that proports to control the 
     cooling level on propane/110V, right?  I'll call it the control valve.
     
     Have you checked the tube from that control valve to the burner to 
     make sure it isn't partly plugged or otherwise restricted (blow 
     through it)?  I could even imagine a scenario in which the tube is 
     accidently crimped (dinged) during a removal/installation.
     
     -Blaine
     '91 Silver Westfalia "Super Chief"