2 door chevy blazer over heating??

I have a 94 cheavy blazer that overheats with the plow up.  I know the truck will obviously run warmer cause the plow is blocking the air flow. but it never used to do this with the plow on. i have replaced the radiator, t stat,and fan clutch all work fine. but the truck still overheats. i dont seem to be losing coolant. so now wat should i look for??

One possibility is that the new 'stat is bad.  Another is retarded timing will cause engine to run warmer.

well im pretty sure the stat is good cause it runs cool when there is no plow on.....and i have been meaning to check thetiming has been running a little slugish.. thanks ill check that and getback to ya