Could be a little high. Do you have the actual TRACTIVE EFFORT numbers from the dyno? TQ at the rear wheels depends on tyre diameter and rear diff ratio, which the dyno guy enters in. When this is crunched with the TE, it spits out a RWTQ number.
ie: RWTQ = TE x r (tyre radius) / diff ratio.
The tractive effort number will be "X Newtons" or "Y Pounds". If you're using lbs, you need to use feet for the tyre diam, and when using Newtons, you'll need to plug in metres.
ie: my 260rwhp XD with 4.11's and 265/50x15's makes 1250 lbs of tractive effort. But at the peak TE rpm (will be same as peak torque), it's only making 215rwhp (needed for other equation below).
So...............RWTQ = 1250 x 1.058ft / 4.11 = 321 ft/lbs of RWTQ
Another calculation can be used below (torque is incestually connected to HP)
TQ = HP x 5252 / rpm
HP = TQ x rpm / 5252
ie: TQ = 215 (hp @ peak tq) x 5252 / 3500 (peak tq rpm) = 320
very close to other reading.
It should be in the ball park.