The 6.5L runs pretty hot. It doesn't take much towing to see the temp gauge climb quickly. In 1997, GM upgraded to dual thermostats and a high-flow water pump. That will help when towing and is a good swap to perform on pre-1997 vehicles.
Also, the stock GM fan clutch is terrible. It does not engage soon enough. I bent the tang on the coiled spring on the clutch so that it now engages as soon as the temp starts to rise. That one mod has helped tremendously on my 1995 6.5L.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter