96 Cutlass Ciera acceleration prob.

[mickeyg77]

Hi everyone, I have a 96 Cutlass Ciera 3.1 that is giving me fits.
As to what it does:When started there is a loud knocking coming from the engine. After it has warmed up, the knocking pretty much subsides. I have thought it might be a collapsed lifter. It has ran like this for over 3 years (before I bought it, lol) and it didnt seem to affect the drivability of the car at all. I did notice that on hills or when normally accelerating to 60mph, that the car will start running as if has a little water in the gas, ie wants to bog down, but if you punch it to WOT it will run smooth for a while. It's almost like it is losing its prime.
Anyway, as for the knocking, it will is barely audible when the the car is running smooth, but as soon as the car bogs down, the knocking gets loud again. I have changed the plugs and wires, fuel filter, and air filter, but it didnt make any difference whatsoever and my gas mileage is running 16mpg instead of 22 to 25 mpg.
I am at a total loss here and I cant think which step to try next. Could all the problem be caused by a collapsed lifter? Any help would be greatly appreciated. Thanks.