Gear selection problem

[Donchusky]

Mine is a 2007 AWD automatic model (without manual). It starts off well but gear fails to select as you speed up. I sped up to 100km/hr, engine roars very high yet gear fails to change. I down shifted from "D" to "S" and there was a change. I still tried out the "L" position and it changed but putting back to "D" it fails to change to a higher gear. By my observation, it appears more like gears 1 and 2 select but it fails to do 3, 4 and 5.

The oil looks good and is properly gauged. I do not know however if there had been an oil change previously and wether the correct oil was used since I just bought it off a friend who has traveled out of country for good. Would this happen if the wrong spec of oil is topped into the gearbox? If so, what would be the proper thing to do to fix the problem?

I haven't done any diagnostic checks yet cause my OBDII reader is in the mail.

Has anyone had this experience? What other cause would be responsible for this kind of problem? Could it have something to do with the TCM? Some local mechanics are suggesting that I change the gearbox completely. I need help please! Thanks guys!