99 S-10 Problem

I have a 99 4.3L S-10. It has roughly 71,000 miles on it. The problem that I am having is that lately it has been having horrible acceleration, it seems like it has lost alot of power. The accelerator feels rather dull, whenever I step on it, it just feels different than it used to, and once again I will mention that the acceleration is horrible, in first gear i usually get up to 13mph, secong gear to 21mph third 40mph fourth 52mph and 5th gear 55 and up. Now this isnt how this truck performed a couple months ago, this has just happened recently. At first I though spark plugs, so I went and bough the best boch + 4 plugs, had them installed at a shop. It felt better for a day, then it started getting worse again...So now im wondering if anyone out there has the same problem Im having and if anyone might know a solution to this. Im losing my mind with this truck, its just one thing after another, getting expensive. Thing I have recently replaced are: New belt, plugs, u-joint, brakes. I guess another thing I should mention is that the clutch feels a bit different than it used to. So if anyone has any ideas, I would be gratefull.

I'd almost think you need a new fuel filter, check the air filter, then while your at it do a tune up, changing the distributer cap, wires, and router.

Your PVC valve could be pluged, and they can be a real power robber.

I can understand that these parts seem expensive, but you'll be getting better milage instantly, which will help offset the price.