Just wondering what the main differences are between the Gen IV and Gen V blocks.
ALso, is the Gen V considered a truck block ?

Primary differences between a Gen IV and Gen V big block:

GenV
One piece rear main seal (instead of two on a GenIV)
Improved oiling
Some changes to cooling passages (make sure to use the right heads / gasket, otherwise coolant will leak into the lifter valleys)
Block was lightened a fair amount, but cylinder wall thickness is not as great max overbore is .040 on GenV blocks where you could easily get 060 or 120 over on a GenIV
Fuel pump boss removed

They aren't necessarily truck blocks though most of them probably came from them. I am not sure if there were higher deck GenVs or not.

Hope this helps.

I just built a gen V 454. I used gen IV heads and gaskets on a V block. So far with no prob. But I have found that if you use V block and heads you must use V gaskets. Like said above there are some cooling passages changes.