I want to know if the vp44 is the same for a 1998.5 to a 2001 or there is difference between?

Only difference could be the High output versus the standard output. All 6 speed manual transmissions were high outputs, all other trucks (5 speed and auto) were standard output, but I believe they are interchangeable 

TFaoro is right.

 

Just the HO and SO series pumps. SO pumps have high volume and HO pumps have higher pressure. Typically most stay to stock standards in replacement unless your aiming to get every last bit of power then most switch to SO pumps.

actually, not quite.

my 2000 is a 6 speed, and standard output. our 6 speed is only 1-1/4 inch input