96 Jeep Grand Cherokee Limited 4WD

My advice to you would be to run an oil system cleaner through the engine for about 500 miles. This should clear out some of the sludge in the engine. Change the oil again after 500 miles and put some lighter weight oil in it as the cold weather can thicken some heavier weight oils. If the oil pressure still does not balance I would advise to take to a mechanic and get the oil pump checked as the screen may be clogged and oil may not be making it up into the heads. If the oil pump is ok then you may be faced with more serious issues as oil passage ways up through the engine and through the heads may be clogged. If these clogs are permantent there is not a whole lot you can do short of pulling the heads and getting them cleaned and machined. Oil sludge treatment would be the first and cheapest alternative. Hope this helps.