I'm running a Giles pump in my '82 NA pickup, and it's the best money I've spent on this vehicle. ANY future VW diesel vehicles I own will have a Giles pump installed - they're that good.
My truck was originally equipped with the stock (1-1) 4 spd trans and stock pump, which limited freeway cruising to ~ 65mph, and it got ~ 35-45 mpg. This thing was screaming at 65 mph on the freeways...
I changed the trans to a 5 spd (.25 reduction on 5th gear) and the stock pump struggled on flat ground anytime I encountered a headwind. I had to run it in 4rth most of the time, where 4rth gear was, again, 1-1...
After installing the Giles pump (I also had my injectors rebuilt at the same time to get max benefit), I can leave it in 5th gear and do not have to down shift anywhere I drive in my area; I can comfortably cruise at 75 mpg; it cold starts at any temperature without having to plug it in (I also ordered the pump "advance" option which really helps with cold starts), and economy is outstanding. I'm averaging between 45-50 mpg without trying. My truck performs very similar to a NA gasser now, but I never anticipated the increase in torque, HP, and fuel economy... I've got a Dodge 3500 Cummins dually as my "big" truck option and other new cars to drive, but this little truck is the most fun, and my favorite, to drive. It's ugly, needs cosmetic work, but everything under it's new and it's extremely reliable and, again, just plain fun to drive, with the Giles pump unit installed.
If you can afford one, a Giles pump is the best investment you can make for these vehicles, and their service is 2nd to none.
Southernman