zenchal26: swapped out tail motor this morning with one known to be good - same result. However, thx again for your suggestion; had hoped it would fix!

will1563: ambient outdoor temp @ flight time is around 80 deg F. The batts do get warm. I swapped out the stock 3-in-1 this morning with a new one - same result. Am skeptical that both my stock lipo's would suffer identical malfunctions @ the exact same time but that now places the stock charger under suspicion. I need to get to my neighbor who's got a voltmeter. We can, at least, check the no-load voltage of freshly charged batts. My son also has a BCPP but I'll wait have to wait until he comes over to swap a few things with his rig
& see if I can isolate the prob. My thanks for your response.

mochaboy: before this little problem the BCPP would ascend like a rocket with stock woodie flats or syms using my stock lipo's. The only weight I added was the 9g G90. On the G90's maiden flights I could tell virtually no difference in the model's ability to hover for a long period or climb vertically (although my 'climbs' are exceedingly puny). Going brushless sounds inviting and I'm rolling it around in the back of my head. Sounds like you did the right thing in your conversion. But being the stubborn old f--t that I am, the BCPP has thrown down the guantlet and now I'll not rest until I find the answer. When that happens, I'll revisit your link & study like a book. I do appreciate your suggestions and thank you for them.