Intermittant loss of top-end speed

[petej]

After only a minute or so, top-end speed (50s) drops significantly to about 30 mph, but not due to the ESC, LiPo, low-voltage safety event. I bring it in, open her up and all looks and feels cool. I disconnect, then reconnect the batteries (which are still full of capacity), seal her up put her back in. Same thing, after a couple of high-speed passes, top speed drops.
Seems there must be something common to both power systems, e.g. the receiver?

Running configuration:
- ESCs: Hobbywing, Seaking 120A
- Motors: Fegaio 380 9xl
- Props: Venom 36mm, 3-blade
- Batteries: Sky LiPo 4S 30C 4000mAh
- Reciever: PB MR3000

Any ideas would be appreciated.

Pete

[petej]

The problem source was a bad/cold solder joint on the ESC (providing BEC power), battery connector. I thought that a bad solder connection would affect only one motor, but it affected both L+R drives.
Problem solved.