is it true need info

the duster is ready for the first long tour it's been on short trip's
we did not build this car ,don't know stall ect. it had 488's in rear changed to 323,s for road .
talking to someone they asked what the stall was & that if it did not run above the stall it would damage the trans.
? how do i find what the stall is in the car
? is this in fact true
took it out last night with gps at 60 mph it was at 2100 rpm
we,ve got one powerfull mach. here and need your help