I actually changed mine about 10,000 miles ago. (Car has 50k now) so that was 40k on a filter. I could *BARELY* blow through it. It was amazingly clogged up. My car starts so much faster now too.
its not hard to change if you have small hands, It took me about 25 minutes when I had the IRS. its in front of the tank mounted kinda above the IRS, its a tight fit. EVIL SVT Did you ever run torco?
only thing different on this car from the factory is 2.76 upper, idlers, jlt rai, exhuast, just recently put on amazon he around 70k miles and a new clutch. there was a guy on modularfords who just hit 130k on the stock block.
The 99 was getting changed every 10-15k miles. My wife's old car was worse than yours when we had it done at 65k for the first time. The car ran like new again.