07 6.0 won.t rev above 3500rpm

I have a friend who has a 07 6.o from a pickup he swamped into a 87 3/4 ton 4 speed manual pickup. He used the motor wiring harness and drive by wire pedal all from the same donor vehicle. The pickup runs great but won't rev past 3500 rpm in park or in gear. He modified his own wiring harness and had somebody put a tune on it to get it running. The motor is stock. he hasn't got a vss hooked up I am looking for suggestions what to look for when I hook HP tuner up. I am new at this so any help would be appreciated.
Thanks Mike

Without seeing the tune file it's tough to say what is limiting the RPM.

Could be an abuse mode. Or an actual rev limiter that didn't get changed.

yea the pickup a couple hours away just looking for ideas on what to check for.
Thanks Mike