I have a 96 GMC Sierra extended cab with the 6.5TD. I've been pleased with
it. I get about 20-22 mpg on the highway empty and about 15-16 towing and
in-town. I bought it used, but I've put 20k miles on it without any engine
problems or overheating (just regular oil changes at the GM dealer for about
$31 every 3k miles). It pulls my 66' Ambassador (28 feet) with ease,
although you don't have as much passing power at Interstate speeds because
of the high RPM's your already running (about 2200 to 2400 at 70 mph).
Jarrod