Advice on buying a D8L

Ran 2 D8L’s yesterday that are for sale @ the same dealership, any advice what to looked for on transmission/torque converter function would be helpful or anything else. What I did notice was both shifted fine all gears forward & reverse , but 1 of them in 1st gear wide open when I give it full brake it would pulled down the rpm’s and stall out the other 1 would pull rpm’s way down almost kill the engine but would not come to a complete stop.
Thanks Jeff

Advice on buying a D8L