im a bit confused as to what you mean in the last sentence of your post, HPI did release the "Rush Evo" before the Firestorm, which was very similar if not almost exactly the same truck.
those .18cvrs were great engines, had one in my T-maxx before i got rid of it. kind of hard to find nowadays though. have a DTX .18 in my little ST truck, IMO .18 is a lot of engine for a 1/10 2wd ST, kind of wish it was a .15 or something.