Help Please with Maytag Washer

We cannot seem to find anyone that has an answer to the problem with our Maytag washer. A couple of weeks ago we noticed water on the floor and black powder residue under the washer. We removed the front panel and watched a wash cycle. The water is spilling over the plastic rim on the top of the tub. We researched the problem, and have checked the hose for blockages and there is no blockage. There are not any items stuck between the tubs. The drain is clear and running fine. We took off the plastic rim and inspected the seal. It appears to be fine and sealing properly. We replaced the belt. The pump appears to be pumping properly. The washer is leveled properly. We are very frustated, Please help! We are wondering about the pressure switch. The water level fills correctly on all selections. Should we replace it? What else could be causing this problem? The washer works fine on small and medium loads. Any suggestions would be appreciated. The washer is not making any strange noises.