3 G's isn't all that much actually. Remember, the crew has lived under 1 G the entire mission, so there's none of this Zero G to 3 G issue. Remember, the SSTV is capable of 5 G's with a full fuel load and is probably capable of at least 15 Gs by this point in the mission. This is due to redundancies BTW. When it's coming in at such high speeds, it only has 1 chance to do these burns. With all the extra rockets, there is a good chance of completing all these burns if you only need 4-6 of them to perform the burn.