1999 Lexus RX 300 timming belt / low oil preshure

Engine Mechanical problem
1999 Lexus RX 300 6 cyl Four Wheel Drive Automatic 148k miles

replaced belt after engine stoped on my wife. Engine started and ran fine (after puting 3 quarts of oil) drove around fine. Gave back to my wife, she drove 15 miles and it hapened again. She stated the oil light came on and she tried to make it home, 2 miles later, same symptoms. I would guess belt jumped again. This time (maybe last time also) she discribed engine started running poor and no power, cams getting sqweezed from lack of oil fluid to the head? Oil sludge? Now after alot of research I guess the engine is prone to it. If im on the rite track, replace oil pump? Manual also talks about filters in the vvi system?