Hi gws1, what fuel are you using? Try something with 25-30% nitro.....Omega or maybe Norvel. If that doesn't help.... you probably have the vmax6 blues. They are notorious for failing to produce enough power for good lift especially in warm-hot weather. They will always run good at first..... when they are cold..... but once they reach operating temp. they loose power. Now there are guys that have good vmax6s and they swear by them...but here is some advice.....if the drive train is plenty free, if there are no air leaks (head, backplate, fuel line, ect.), the glow plug is good, and the higher nitro fuel still doesn't help.......then upgrade to the vmax7. It flies great no matter how hot the weather......plenty of power! But beware that there has been a manufacturer's defect that shows up in the the vmax7 at a fairly high interval.....causing connecting rod failure. Do a search on vmax7 in this forum and you can read all about it. But all things considered.....the vmax7 is still your best move. I hope this helps,
Mark