Engine replacement

There really isn't a cut and dry answer, it would depend on what you are replacing it with.

Complete engine with transfer of parts is approx 15 hrs of labor

A long block with transfer of "Sheet metal" and parts is approx 23 hrs of labor.

A short block with transfer of cylinder heads and all other parts is approx 24 hrs.

The parts you use are an entirely different issue once again. I would suggest calling around for different prices depending an what you prefer to use. If investing the money in the truck I would use a GM replacement engine, they have good warranties (Nationwide) and are new not re-manufactured. The price on these can vary depending on the volume of parts the dealer moves, so calling around could save you some money