My Tahoe is sputtering and stalling at.

Hi, my tahoe is sputtering and stalling at lights and in traffic. It started doing this about a month ago. I since then have changed: air filter, plugs, wires, cap, roter, coil, fuel filter, and swapped out the computer with a used computer. After all of this, nothing changed. My brother (backyard mechanic) decided to advance the timing (you know, by loosening the distributor and slightly turning). After that, the truck ran much better. Approx. Two weeks go by and I drive it to work everyday, it starts doing it again. I aask my brother what's up? He trys advancing it again, but no luck. The sputter problem is out of control, the truck stalls, and when I try to kick it into passing gear, it actually slows down. It takes a few tries to get it started now. It will turn over about 3-4 times before sputtering to run (and that is with me giving it gas to keep it running, but only at first-it idles after that). This truck is in great condition for having over 200,000 miles. I have had it serviced and have been told haw great of shape it is in. My brother told me I may need a new timing chain installed. *Sigh* I know that is expensive. I just want to try and rule some other things out. What do you think?