00' GP SE loses horsepower...

I strongly believe after the oil change on sunday, and recently placed fuel injector cleaner, I feel as if my 00' GP SE V6 3.1L w/ 120094km is not as fast before. When I accelerate on the pedal the car is not going fast like it was before the recently job. What might probably cause it? the rpms idle b/w 1-2 at rest>stop, but when I stomp on the gas pedal it goes from that range to 3-5 rpm. Any advice would be help far as restore horsepower or any info?

is the fuel injector cleaner still in your gas tank? That might be slowing it down some.

Hi,

As of matter of fact, the fuel injector cleaner is still in the gas tank. So are you saying after the gas tank is almost empty > once the fuel injector cleaner is dissolve. Then the horsepower would come back