Toyota Repair: shifting problem, shifting into overdrive, hydraulic pressure

Question
Sir, I have a 2002 tacoma extra-cab 2x2 4 cyl. automatic with 118,000 miles. Recently it has not been shifting into over-drive. When it does it comes back out into lower gear.I changed fluid to no result. Any ideas. Also doesnt hit over-drive until 70 mph

Answer
Are there any warning lights on the dash on? Is the fluid level correct and is the correct atf fluid in the transmission? In most cases not shifting into overdrive until higher speeds is due to a hydraulic pressure loss which may be an indication that the transmission is starting to fail.