I saw a TRex 600 on the bench at the LHS, he had a battery problem, it was going to cost him like 300 dollars, because he flew 30 seconds too long...but yes, big and awesome, I'd like to see one fly.

Cmdr. Bob, I don't think the weight would make that much difference--if you didn't change anything else, I would suspect that the gyro might be drawing more current than we would expect. First thing I'd try would be to unplug the gyro but leave it on the heli, wire up the tail like normal, and see if it still won't climb out.

If we can eliminate the gyro as the problem, then the next thing would be to increase pitch a little. Whether to use the pitch links or the servo link rods will depend on the travel limit of the head. Look at how the part called the "rotor head" slides on the center hub. The upper and lower limits of the travel here are what you have to watch for. The servo rods should be set so that you are just clear of the stops at the top and bottom for low stick and high stick in idle up. Usually if you use the servo rods to raise the pitch very much you will wind up binding at the bottom travel of the head. But this depends on , like, where it's at right now, you dig man?
I prefer to use the servo rods to raise the pitch if it's just a hair, say 2 full turns max, because it just is easier, bearing in mind the binding thing I mentioned above. You can use the pitch links of course, but this may require retracking, and those things are so darn small...
Usually you will wind up using a combination of both to get it really right.
But as a first pass, adjust each of the three servo link rods, or and/or the two pitch links, equally and by full turns (the sockets fit better one way.)