SC10 4x4 FT - Drive train issues

[Randall34]

I'm building a SC10 4x4 FT, after building the gearbox casings up i noticed that they don't really run very freely, the diff/idler/topshaft seems to have tight spots, thought i'd carry on and see what it is like after a few runs. However now i have introduced the belt and the whole drivetrain seems to be very resistant. Has anyone got any advice, the belt drives i've had in the past have at least free wheeled (with no motor) this doesn't, so i thought i'd ask you before running it.
Please help.
Cheers
Neil