The engine code is related to the Knock Sensor. It is a bit amazing how lazy/uninformed some mechanics still are, especially with the internet. It is well known throughout the Toyota community and most mechanics that work on Toyota's that you must replace the knock sensor/KS wire and how you must use new head bolts when working on the 3.0. The KS wire runs right along the head and gets brittle from the heat, and is why it needs to be replaced, Toyota recommends replacing the KS as well due to its location.

The reason it wont run over 75 is the ecu isn't getting any feedback from the KS and retards the timing to prevent engine damage at higher RPM's, it should normally come on at about 2500-2800rpms.

I would suggest he pick up a code reader for about $30 and check the codes himself. As long as the code comes up for KS, he should be fine, just tell him not to run the engine at high rpm's until he gets the KS replaced.

When he gets back, take the truck back to the mechanic and demand he put a new KS and KS wire in, and if he didn't use new headbolts demand he install new ones. The 3.0 head bolts are torque-to-yield bolts and are a one time use only bolt. The reason for this is that the bolt is designed to stretch during the torque process(diff process than normal head bolts), the stretching process makes it impossible to get the same torque value once they are loosened, and reusing TTY head bolts is a guarantee of head gasket failure in the short term future. You should expect to pay for the KS/KS wire and new head bolts(if nec.), but not the labor to install, labor cost is the mechanics loss for not properly rebuilding the engine to start with.