it may take a while for gas that has been sitting around for a couple of years in the system. That being said, after your timing chain job, how did you set the ignition timing? Did you use a scanner and go into fixed timing mode after the engine was warmed up to normal operating temp? With the scanner on Fixed timing the timing should show 5 btdc on the scanner and then the actual timing should be set to 5 btdc. (in park or neutral with parking brake on, normal operating temp.)
Have you had a scanner hooked up and see how the computer cam and crank sensors
are looking? Have you tried to see if the MAF is showing a normal air flow at idle? At idle with normal operating temp MAF signal should be about 2.0 volt. at 4000 rmp it should fear about 5.0 volts.
You might want to check the operation of the idle control valve. Does the scanner show that it is working?