2001 jeep grand cherokee. no leaks losing coolant,

Most serious item I see is oil pressure. Put a mechanical gauge on the engine and get an accurate reading. Also make sure that the passage to the sender isn't blocked. If you did the pump yourself, did you find any coolant in the oil? In 99% of all low oil pressure situations, the oil pump has not failed. Rather, either a cam bearing or crank/rod bearing is worn. You do not have to have one spun or completely worn out bearing. Even wear of all bearings that is somewhat excessive can bleed off enough pressure to cause problems (plastigage the engine bearings to determine wear).
As far as coolant loss. A cylinder head gasket can fail between cylinders, into a water passage, into an oil passage or any combination of those and externally as well. The cylinder heads on engines beginning in about '98 are prone to "micro-cracking" which can lead to all kinds of hard to diagnose coolant loss problems. It may help if you have a shop do a dye test and a hydrocarbon test on the cooling system and see what they find.
I have seen several kinds of block sealing systems available. Though I generally do not recommend them, as the longevity of the repair isn't predictable, you could try that as a option of last resort.
There is no quick easy solution to your problem but with a bit of "poking around" you may be able to cure it. Don't bother repairing one problem before finding out what the other one is first though as together, it might be smarter to replace the engine.