Possible causes, improper break in, improper tune, wrong fuel type, dirt getting around filter foam or a torn filter neck.
Since your on engine-P/S #2 and you have the exact same issue as #1 the problem is either with the parts on the truck(air filter/neck) fuel type or tune.
I would give the air filter and the rubber a really close look over.
Did you use anything to secure the filter neck to the carb?
Are you using car/truck fuel and who makes it and what nitro content?
How are your tuning skills, did you tune both the HSN & LSN?
It has to be something simple, two P/S's just don't get trashed in under a gallon each without a reason, be it a truck parts problem or operator error.