1992 Other Hyundai Models car hesitates

I have a 1992 hyundai excel that has about 86k miles. Car drives good with excellent power for a short time. After about 20-30 miles it looses all power pull off to the side because car will not go anywhere. Now i turn off the car for 1 minute turn it over and power is back for 4-7 miles starts again looses power. Now after so long it just looses it power all together and have to let it sit for a long time. Now i checked the timing on the car and seems the timing is off by 10 degrees. I dont know how to change the mechanical timing but i adjusted it on the computer side. When i did that adjustment it worked for a short time then the issue came back. Do you think its a bad timing belt or just need to get the mechanical timing change to fix this issue or could it be something else. Its a 1.5L engine but im pretty sure its a mitsubishi motor with hyundai logo on it. If anyone has any idea or suggestions on this it would be appreciated. thanks