When I start my truck it turns over slow as if the batteries were low. The batteries are brand new but I checked them individually just to make sure they were both holding a charge. If I keep cranking it over the starter will speed up and crack over like normal. Does anyone have any idea what's causing the problem.

 

Anything getting hot? If the cables are on fire that's a problem, check all the connections. Any heat is a power loss. If the starter is super hot it could be going out but often times they are over loaded. Any other problems that could make your engine hard to crank? I've had seized AC compressors and it's possible that an injector could fill your cylinder with a lot of fuel and try to hydro lock it. Could make sense if you start it then it cranks fine.