Loosing pressure
 

Hey i have a 91 xj, i recently noticed that my 4.0 ho engine is at 800rpm when idle... thing is,when going downhill i used to shift 2nd gear and rpm goes to 2000rpm... when it reaches 1000 rpm it automaticaly shifts to 1st gear... now with low pressure when running downhill the engine is always at 1000rpm and when i shift from 3rd to 2nd gear it shifts directly all of a sudden to 1st.. does this trans.case issue related to engine pressure drop?? When checking oil dipstick it shows level half inch above the SAFE area... i used to see the level 2inches above safe area knowing that i put 6 quarts when last oil change. Any thoughts ??