I had the fuel lines recently replace on my 2004 Buick Rendezvous, now when I

It's so hard to know what you'd be experiencing your symptoms, based alone on the replacement of "fuel lines". There are too many variables, too much unknown. Testing would be required to check fuel pressure at the fuel rail at the engine. Checking exhaust flow, air intake, ignition spark, engine timing and compression. Performing testing will reveal a source of concern, and you'll have to approach that.