Would I need to do a SAS on my 88 pickup if I wanted to run bigger tires and do a little bit of serious mudding. It is a daily driver so my mudding wouldn't be a balls to wall kind of deal.

 

Your 88 front end will not take kindly to larger tires and mudding. Adding a locker to the front will increase your chances of breaking a cv axle 3 fold.
33" will fit with minimal trouble but they do offer a greater strain on the steering components. It all comes down to what you call "a little bit of serious mudding".