Kennedy Diesel,KOJO,Heath Diesel are all great OBDII tuners.
SS Diesel just re-sells a Westers Garage tune that by most reports is out of date.

For OBD1 Buddy Tune 6 banger chip is the way to go.

kojo has an upgraded turbo and tune for like 1000 dollars. which sounds pretty nice

I like the 6.5 too. But this motor is better left closer to stock. With exception of intake and exhaust. Once boost and or fuel is increased it will increase cylinder pressure as well as egts. It wont be a matter of if but when the pistons will crack drop a valve ot blow a head gasket regardless of what billy says with arp studs or not. :argh:

With the electronic IP's there are endurance gains to be made with tuning because with proper boost and fuel mapping EGT's can actually be reduced provided intake and exhaust are up to snuff.

The Kojo Tune Is Awesome Just Put It In And Love it

after a few days of driving with the kojo tun i notice a few more things after i can keep my foot out of it. First thing is the transmission locks up sooner,probabaly 5mph sooner but it is right where i drive everyday. I have more black smoke until the turbo catches up then i have almost no smoke at all. it is smoother through all the gears.

I love my heath chip. And I also love that "kojo" turbo you guys were talkin about. Heath is the #1 for 6.5's he makes quality products. SSD is crap. Their "tune" is a Wester's tune with an SSD sticker on it. Heath actually makes his own tunes with plenty of testing.