Does anyone has any ideas where I might look to troubleshoot the problems my heli's having?
After well over 50 flights one day it just suddenly lost a heap of power and became very difficult to control the yaw. It happenned within about two flights. Everything was fine then one morning I took it out to fly and it couldn't hold the yaw rate steady at all and it seemed like I had to have the collective way higher than before just to hover.
Because of the tail I thought I might have finally burnt out my tail motor, and since I had an airframe replacement I transplanted the 4-in-1 and servos over to the new airframe (making reference to bdavidson's assembly thread) but the problem is still there.
What's more when I do hover I have barely any cyclic authority, it's very very sluggish responding especially to roll commands.

I thought I might have the blade pitch off leading to a head speed that was either too high or too low, but if I decrease the main blade pitch any I can't get off the ground even at full collective/throttle and if I increase it more than 2 half turns of the pitch links I can hear that the head speed's too low as it struggles to overcome the extra torque when it does fly.

I've been using the same two NiMh battery packs for at least the last month, and I did have the helo in my trunk for a few hours at about zero C, is it possible that it's actually the batteries that have both crapped out because I froze them, or is there maybe a problem with the 4-in-1? After a full charge I still get around 8-10 minutes of flight out of each of the battery packs.

I've spent several flights tweaking the main blade pitch back and forth and checked that there's no binding when I hit the extreme ends of the collective and cyclic commands. When it does hover the helicopter itself is still fairly stable, I can leave the cyclic alone for a few seconds before I need to put in corrective input, but it's just so unresponsive it's very difficult to control compared to before and I'd swear that it has a tendency to pitch forward a bit when I try to roll in one direction, where it didn't before.

I love this little thing and was just starting to get warmed up with some real flight, any help would be appreciated.
THanks