Timing Problem

[miste2k1]

I have a 1990 Eagle Talon with an engine in it out of a 1991 Mitsubishi Galant. It is a 2.0 Liter DOHC non turbo. The timing has jumped on this car three times. The belt was replaced the first time and the car jumped again and the mechanic put it back in time thinking he didnt get it just right somehow and it jumped again. This time he replaced the Hydraulic part of the tensioner ( with a mitsubishi dealership part ). The car was drove for appx. 100 miles and the timing jumped again. The belt on the car is a dayco belt from advance auto parts. I was told that since it was not a dealership belt that was the reason for it jumping time? Is this correct? Is the dealership belt better and will fix my problem or will I be in the same problem but with more money spent? Help please!!!