Question on servo's.
 

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?

The twitching sound your hearing is common with digital servos 'centering' themselves, and is quiet normal.

I would completely disconnect the linkage from the futaba servo, and see if it improves. If it sound improves dramatically and goes away completely, then you know your linkage setup is binding or needs adjusting (ie. throttle or brake links could be pushing up/down on the servo horn etc)