Rip cutting a length of hardwood like oak is a much tougher job than cross cutting and you're trying to cut through a very thick piece. Note this is dangerous on a table saw, and especially if there's high feed resistance. Do not push harder to feed faster hoping to avoid the burn marks! Instead, you have to avoid the situation that is overworking your blade and/or motor.
You say it's a new blade so it's probably not gummed up with pitch yet and it hopefully is still sharp. Many hardwood species will burn (get the black scorch marks) if the blade is binding and cutting too slowly or if your feed rate is too slow. Species like cherry are very susceptible to this.
You say it's hard to feed, so you likely have one or more of these situations, some of which have already been mentioned:
- Not the best blade for this job. A dedicated carbide rip blade will do better. If you really want an all-purpose table saw blade, the Forrest Woodworker II series are fantastic. Their performance and incredible support made it worth every penny.
- Not enough power in the saw motor, so it is bogging down and the blade isn't running full speed. What is your saw model?
- The wood is binding, which can get pinched between the fence and blade or between fence and guard splitter if they aren't aligned right
- The wood may be pinching the blade itself if it isn't properly seasoned or has warp stress being released by the cut.
- Make sure the blade isn't warped, damaged, or dull.
- Make sure the saw itself isn't vibrating excessively.
Assuming you have already thickness-planed the oak, one way to do this kind of cut is to set your blade height to just barely more than half the thickness and run it through once on each side. This is easier for any blade and table saw to handle. Note that for the FIRST pass you have to have most types of blade guards removed (but it's an embedded cut), but you should still replace the guard before the flip cut since it can pass the splitter.
By the way, although it is certainly feasible to make that cut on most table saws with the right blade, it would be vastly easier and also far safer to make thick rip cuts like that on a band saw.