yeah my money would be on an air leak. make sure all your fuel connections are tight, and that the carb is secure to the crankcase. if youre running an external fuel filter make sure its tight.
seems to me, i read a post somewhere about traxxas fuel tanks cracking just a tiny tiny bit around the screw holes, which was causing tiny airleaks. the dude had similar symptoms to yours. he replaced his fuel tank and was fine! so check and make sure the fuel system is good n snug.
i had a similar problem, and that article promted me to check my car good, and it turned out the fitting on the fuel tank for the line to the carb was loose, and air was getting in. replaced the fuel tank and viola.
p.s. any nitro car will wander forward at idle, unless you have a good clutch. every nitro car ive ever seen save for a few with mip clutches do it. could flip your clutch shoes around so they slip a bit more, or just use the brake