I just bought two Firestorms (one for each of my boys) last Monday, one had a major mishap, the controller malfunctioned and the truck took off and smoked a curb at full speed. That one is on its way back to HPI.
The other one runs great, had to do some adjusting rather the pro at the hobby shop did as I have no clue what I am doing. First trucks for me, but so far I love the truck. Runs hard, handles really well, suspension always trying to keep wheels on the ground. It literally rocked my buddy and his kids Team Assoc. RC10GT2RS out of the hole, wasnt even close.
All that being said, it sounds to me that you are having the same problem I was having, in that it is running too rich. The guy at the hobby shop should have been able to fix this when you had it in. I am no where near experienced enough to tell you how to fix it, so I would venture back to the shop and ask them to set it up. Mine did free of charge while showing me how to do it and what to look and listen for.
Overall so far I think they are awesome trucks and cant wait to hit the track. Good Luck.