First off ,you "HAVE" to clean with W&G remover and to apply it you have to get the paper shop towels dripping wet then wipe the panel,wipe it off while the panel is still wet. one panel at a time
Think of it as the wet app. melts wax&grease the second wipes it off ,if its not wiped off the wax & grease soilidifies and remains on the panel.
secondly,it sounds to me like you have some kind of contamination coming from the compressor (a very common problem) You need some filters and also a disposable filter at the gun.Theres three must have filters you need for painting , 1st is a water seperator then a paper filterthat gets solids like rust etc and finally one to get the last little bit of moisture called a desicant filter Filters can be expensive even ridiculasly so...Id suggest going to harbor frieght and getting them since your painting all the time...you can also make them ....You'll never get good,clean paint without good,clean air and thats on top of a good ,clean surface....
OK,lets talk about heat... kero torpedos will cause problems if your using an open flame type heat use propane only...its the exhaust.,kero is bad enough but diesel exhaust is about the worst for contaminating the surfaces