In my opinion, using a jointer requires the most "technique" of any woodworking tool, and far more than most people suspect. And I always cringe when I hear the word "pressure" in describing the use of a jointer.
But first of all, let me say I've been using the same Rigid jointer you have for about 4 years. They come out of the box with the infeed and outfeed tables perfectly set up at the factory, and I've NEVER touched the table adjustments in all that time. And it seems that in nearly ever post regarding jointers, people always suggest screwing around with the table heights as the solution to any jointing problem. After all, it MUST be the machine and not how I'm using it!!!!
Not so! Look at how the tables are held in place from the factory. They're pretty darn solidly kept in place, and I doubt dropping one from 20 to the ground would in any way affect the heights of the tables. Do you think that in just normal use the tables are actually going to go out of whack??
Over the years I've found that the "pressure" needed to joint stuff correctly is really, really light. Just enough to keep the wood from hopping when it hits the knives, especially when face jointing. You be surprised how much you can flex lumber, again especially when face jointing. I use a "rule of thumb" when jointing - I only apply pressure to the outfeed side with my thumb, and then only about 20% of the pressure I COULD apply with my thumb. On the infeed side I only use horizontal pressure to feed the piece thru.
The theory of the jointer is to pass the material over the knives and let them take off the "high spots," if you will, until the knives reach the "low" spot on that face (or edge.) Putting any downward pressure will have to distort that theory, and the wood.
So my suggestion is that you're right in assuming it's the pressure impeding the feed. I've cleaned and waxed my tables and it works like a charm. Try experimenting with decreasing amounts of any pressure and you'll eventually find the minimal amount of pressure needed to accurately joint stuff. You'll be surprised.