Q: Changed heads. Engine runs great until I put it in gear, then I have no power from transmission, shifts hard, and breaks are hard.

Hey there. Given that you performed a fair amount of engine work and have no doubts with the battery out of the car, it is possible that the throttle position sensor and engine management have lost their "pairing" values and an "idling re-learn routine" is in order. After disconnecting the battery, wait 10 minutes, reconnect battery, start engine, put in gear Drive for 1 minute (idling), put in Reverse 1 minute (idling), and drive moderately for 5-10 minutes. After that, idle re-learn should be complete.

It is also possible that given your mileage, the throttle position sensor is simply failing. The TPS affects both engine power and shift quality since the transmission takes signals from it for upshifting.

The "stiff brake pedal" sounds like the vacuum line to the brake booster was not properly re-connected, or one of the vacuum/vent valves in the brake booster has failed.

If you would like to have this all scoped out for you, a certified technician from YourMechanic can come to your car’s location to diagnose the loss of power, shifting problem, and hard brakes in person so that this can be corrected.