Playing double bass is an acquired skill and takes a ton of practice. I currently have 5, direct drive bass pedals that I play, 2 Pearl Demon Drives on the Strike module, a Trick BigFoot on the Sample pad Pro, a Drumnetics on the Strike multipad, and another Trick BigFoot on the Yamaha DTXMultipad.
Typically, you would want as much "bounce back" as you could get as this signifies there are no friction points in the bearings or hinges plus the quicker the pedal comes back, the quicker you can get it moving forward again.
I use "QuickTorque" cams on my Demon drives with almost no spring tension at all so the pedal bounces back as quickly as possible.
Another common complaint is if you are using a driveshaft between the pedals, the slave side is typically not as responsive as the master side.(the Trick drive shafts being the exception).
If you have the spring tension as tight as it could go, that could be your problem. The tighter the spring, the quicker the return of the beater off of the head or pad.
Keeping pressure on the pedal between beats effectively keeping the beater against the head is known as "burying the beater" and is somewhat frowned upon as a bad practice to get into.
If it were me, I would loosen up the spring tension considerably and then practice different foot placements on the pedal to get the best feel/response for the speed with which you want to play.
For example, I like the "slide technique" where you play the first initial beat with your toes near the center of the pedal board, slightly lifting off of the board as it returns and sliding your foot forward to catch the board as it's returning to play additional beats. I find I can play pretty fast like this as well as play intricate patterns.
Others use the "heel toe technique" which I have been practicing here lately but it is not as easy for me as the slide technique.
You could also play around with how far back you like the beater off the head at rest and at the beginning of the stroke. This is just a simple adjustment but it usually takes a bit of time to find the sweetspot for you which may be different for others.
Todays modern pedals have so many different adjustments available it can be overwhelming at first to find just the right set up and foot technique that works for you.
By playing single bass for a few months, you've trained yourself to play one way and now you've added another dynamic where you will have to retrain your muscle memory. Single bass, you typically have one foot on the floor at all times either the bass or hihat helping you to keep your balance. With double bass, I have a hard time keeping my balance since both feet are off the floor. This is a posture and core strength issue that I fight all the time and I find that I concentrate too hard on trying to keep my balance which throws off my timing.
Having never played RockBand, I don't know if playing doubles is the same as playing on the Surge kit.
Hope this helps you.
powerhouse