One thing that helped me beat Green Grass And High Tides so I wasnt playing just GGaHT over and over was.... if you have a real guitar practice the button combinations on the strings with the corresponding finger to color parallels meaning.. fingers 12344.. colors GRYBO.. I would transit and start by practicing 123212321232123 over and over again then switch to 23432343234.. then back to 12321232123... to etc.. You can also add these combinations for more advanced practice... 1343134134.. to... 124212421... (helps w/ Free Bird) You can do this on any string, strum, no strum or both can be practiced with any combination. If it doesnt sound right move to a different string/fret. Make sure you practice hitting the notes accurately before focusing on hitting the notes faster. Speed will come through time with good practice. Its a win win as it also helps you learn/practice basic motions of scales and will help with the transition to Pro Guitar. Always combine this practice method with switching back and forth to Rock Band (GGaHT, I also played Franklin's Tower) and real guitar. This will get your fingers moving much better and take away some of the grind time on the ONE song!
Also, for the first two sets of snakes focus primarily on the descending notes (321.. BRG 321.. BRG) always strumming the Blue/3. When you go back to the 3 you will sometimes naturally hit the 2 if you begin to roll it properly. Using this practice method I personally got to the point where I could almost do all snakes without any star power. For some reason the last snake was the easiest for me so I have no advice except for let your fingers roll freely! I personally went to master GGaHT first in the last tier simply because if you get GGaHT everything else is a breeze. Repetition is Key, Dont Give Up!