Why do the aftermarket fuel pump assy I see have a "new style" electric connector? I would really rather not hack up my harness.

 

The stock harness has been known to have problems with heat and/or corrosion. The new pumps come with a revised connector to fix these known issues. Not every original style connector has these problems, but it is a good idea to use the redesigned connector. Just use some 3M butt connectors or solder & heat shrink the splices. I really like the 3M butt connectors as they have adhesive in the heat shrink tubing on the connector for a nicely sealed connection.

 

and put some dielectric grease in the contacts of the plug , keeps the moisture out of it and transfers heat in the case of a weak connection which has always been the issue with the gm trucks