I don't think the problem is the thrust angle.

When you say you have everything trimmed out right, what is your method of determining what is right? If everything is right, you should not need more down thrust than the manufacturer builds in.

You probably just need some down trim on the elevator. For some reason, a lot of models need the elevator to be trimmed down somewhat relative to the stab, i.e., in neutral trim, the elevator might need to angle slightly down. How should the elevator be trimmed? Well, if it is climbing too much, give it some down trim. If you get it trimmed for level flight in a cruise, then it should take off OK.

After you get it trimmed for level flight in a cruise, then how does it behave at other speeds? It should climb with more throttle and descend with less throttle. If it climbs too much with full power and falls too fast at low throttle, then the balance point is too far forward. If the balance point is too far forward then the elevator trim that gives a good cruise will be too far off at other speeds. Check you balance point carefully.

Jim