There is a lot of info on this site regarding timing of the 6.5. The one thing that I ran into was that the engine has to be up to I believe 185 degrees before the timing will take. I also remember that I had to sometimes increase the engine speed to get the setting where I needed it. Again I would suggest that you do a search on this site for timing of the 6.5 and you will get some great information.
1995 Chev 4X4 1500 Suburban 6.5 TD,Phazer Gear Kit from JK, High Capacity Water Pump Kit from JK. Special Calibration fan clutch W/8 blade fan from JK
1995 Chev 4X4 2500 Suburban 6.5 TD>>SOL-D (parts car)
1999 Chev 4X4 2500 Suburban 454 "Gas Hog" with Hiniker C-Plow