I have this problem also, and here is how I solve it.
1. I do not use mulching blades. I understand the purpose, but I've never had good results. I use the blades with a slight lift. Nothing radical. It's just a personal preference based on what has worked well compared to any other "exotic" blades. Simple light light blades.
2. if the grass is wet (sometimes unavoidable as I have a very large piece of property that must be cut rain or shine every single day), then I make two passes. the initial higher pass and another at the lower level. I do not follow the same line. It takes longer but that is what it takes sometimes to get a good clean even cut...sometimes working the second flight at 45 degrees!
3. I keep the blades sharp DAILY. Your mileage may vary, but one of the keys to a good cut and proper discharge = sharp blades! Make sure also the belt is NOT SLIPPING. check that belt pulley tensioner. If the belt is slipping, you end up cutting but not properly discharging. You want those blades to cut fast and keep the momentum to move it OUT!
4. A slight deck tilt that is lower in the front than the back is a good way to make a very clean cut..However, if that pitch angle is TOO sharp, then you end up "digging" and that can create buildup. For my 60 inch deck, the pitch is only 1/3 inch less in front than rear. That's all it really needs. Anything more than that and you run the risk of "carving" and the cut grass isn't getting ejected correctly.
5. always check the tire pressure in front and rear...if you have front tires flat or leaking, this will change the pitch of the deck.