Perhaps the Hi-Tecs are an issue, but I've been flying several 127DFs with Futaba digital servos for several years. I fly these airplanes aggressively, though not 3F (flip flop flying), hovering, etc. I have helicopters for that sort of thing. I have yet to see any problems with these airplanes.

Another possibility is your battery isn't strong enough. It has been shown in some helicopters that certain NiMH batteries indeed do NOT have enough voltage to reliably move digital servos under a heavy load; such as 3F "flying". As far as I'm concerned, the jury is still out on this one, but there are enough experienced guys who believe it for me not to dismiss it out of hand.

However, I do NOT think your problem is directly attributable to the R127DF receiver. Try a large-capacity ni-cad battery and run your test again.