96 Suburban confusion-----

[Tracktor]

I just picked up a '96 GMC Sub SLT fully loaded 117k in excellent condition for $6500. I bought it for a daily driver. I already have a 98 K3500 Crew-cab 4x4 for towing so I am relatively familiar with the 6.5TD. Here is where my confusion comes in-

1) I wanted 3.73s in the Sub for better mileage. When I test drove it it ran about 63mph at 2000 rpm my 98 cc runs 55mph at 2000rpm with 4.10's so I figured I was good to go. When I got home and checked the RPO #'s they both say 4.10's? Any ideas what is going on here?

2) I wanted to do the dual thermostat upgrade first thing but the housing on the '96 looks identical to the '98? I haven't cracked it yet as I figured I'd ask first.

I didn't research more before the purchase as I had given up on finding one for and was looking at gassers. I figured I could unload this one if I didn't like it as it was good deal.
Thanks for any advice..........

[More Power]

I just picked up a '96 GMC Sub SLT fully loaded 117k in excellent condition for $6500. I bought it for a daily driver. I already have a 98 K3500 Crew-cab 4x4 for towing so I am relatively familiar with the 6.5TD. Here is where my confusion comes in-

1) I wanted 3.73s in the Sub for better mileage. When I test drove it it ran about 63mph at 2000 rpm my 98 cc runs 55mph at 2000rpm with 4.10's so I figured I was good to go. When I got home and checked the RPO #'s they both say 4.10's? Any ideas what is going on here?

2) I wanted to do the dual thermostat upgrade first thing but the housing on the '96 looks identical to the '98? I haven't cracked it yet as I figured I'd ask first.

I didn't research more before the purchase as I had given up on finding one for and was looking at gassers. I figured I could unload this one if I didn't like it as it was good deal.
Thanks for any advice..........

The alternator provides the tach signal. Not many 6.5's these days are running the factory original alternator, which means they likely have a replacement alternator with the wrong diameter pulley. The diesel pulley is unique.

GM incorporated the hi-cap cooling system in the late 1996 model year, and there was a short transition period where some, but not all, of the hi-cap parts were used for a brief period of production.

I saw a 1996 6.5 today that didn't have any of the hi-cap parts.

Jim

[Tracktor]

Thanks for the answers. Do you know offhand what diameter the pulley should be? I've replaced the alt on the pickup awhile back & would like to check to make sure of the size.........