In terms of throttle and steering servos, is it okay/safe to run two different brand name servo's for each action?

Bought an XTM XST rtr kit about a year ago. Has siruis servos and the 24.7 engine in it. The steering servo died and I replaced with a "hitec" I believe it was, and have had zero problems. Now couple months later the throttle servo has gone south. Replaced it with a fubata.

What I have noticed: It will make a twitching sound when its sitting on the floor with the reciever on. If I turn the reciever off, it will stop twitching.

I have probably a good 80 ft of range now and the car will loose complete control. Where should I start, or should I go back to the first question?