Driveshaft critical speed

[LeesTruk]

I'm putting a mild 4.8L/4L60E into my '89 Cheyenne. I'll be taking it to be dyno tuned, probably this summer. My concern is, "how fast do the tuners usually take a vehicle on the dyno drum?" I want to be sure that the stock driveshaft won't turn into a pretzel at some unfathomable speed that the truck will never see otherwise. I'm considering having a 3.5" shaft made, either steel or aluminum, but if the stock shaft will handle a few pulls, then maybe I'll keep it. If anyone kinda knows the answer to this, please let me know. Thanks

BTW, the truck has a 3.08 gear, and the little 4.8 likes to make some high rev's. The cam I'm running is a TS&P stg. 1 truck cam (208/214 @ .550 lift).