Rather than make a decision based on opinions, why not actually troubleshoot it instead of throwing money at it. First off, do a compression test both dry and wet. Post up pix of the spark plugs. Do a vacuum test, both at ideal and at 3500 rpms in neutral.
Grab a timing light and measure the timing at idle and 3000 rpms.
Get a loaner pressure gauge at Autozone and measure the fuel pressure both at idle and at speed under load.
Take a pix of the tail pipe for soot etc.
Post up your results and I/we can help tell you what is going on with the engine. All the gauges you need are available on the loaner program at Autozone. If you need help in performing the tests, post up and I/we will instruct you step by step.