1999 Chevy Lumina cars dies as I take foot off gas

That mechanic doesn't know what he/she's talking about.

Trained technicians never, ever replace parts until we find what's wrong.

The proper way to diagnose a drivability problem is to isolate the system at fault (ignition/fuel/mechanical, etc.) Then test each component in a logical manner until we find the cause.

And even if your computer isn't setting any codes, a trained technician will do a "Drive Test" with the scanner hooked to your computer so that he/she can watch in real-time what your engine and its systems are doing.

Now, your issue sounds like a vacuum leak, but there's no way for me to determine this for sure. You can also have faulty sensor, such as a throttle position or mass air flow sensor.

But your best option is to take your vehicle to a competent mechanic who has experience with "Engine Performance" diagnostics.

Yes, a good mechanic costs good money. But if you "Replace" parts until you find the cause, I guarantee you that you'll spend waaay more money than just having a competent mechanic do it right the first time.

If you're too low on cash, here's a little consumer secret that the industry would be pretty mad about if I tell you.

Find an established shop that'll give you a free estimate.

What they'll do is diagnose your issue until they isolate the cause, then the service writer will make an order for a fix.

Then you write me back, and if it's a simple procedure, I'll walk you through fixing it yourself. Or you can find a buddy who's handy with a wrench and pay him to do it for you.