Can anyone give a steer to a person or company inside the USA who can evaluate TT engines and/or repair them?

I have a fairly new TT engine (bought used so no papers) that has little run time but will not run reliably without quitting (and for no apparent reason.... sometimes a low throttle/rpm and sometimes at high throttle/rpm. I've looked at and tried all the suggestions from modeling friends without any success but probably really need to send this off and have some more expert person/company have a look.

Any specific information on where to send this will be greatly appreciated