l have a 2000 Mercury Grand Marquis GS with a h-pipe 2'' dual exhaust, and two 2.25'' flowmaster super 44 mufflers. l also have teh K&N cold air intake. About how much horsepower and torqe do l have now on ym current setup? And what can be done to get more horsepower and torque?

You could add a chip or reprogram the one that you have. You will have to use hi-test gas from then on.

ummmm go get better oil

Bellieve it or not, the car is computer controlled & all that stuff was a waste of money. The car senses too much air & compensates by setting back the performance a little. u & 99 percent of the consumers of those gimmicks only think u have gained some power. You got not as much--the manufacturers got the money. You can try resetting the computer--disconnect the battery pos & neg for 15 minutes--restore it all & u may get a difference but this works even without all the after market stuff. l did this with my 99 Suburban--now it runs like new again--what a surprise l got. 19-20 mpg & pretty peppy for 145000 miles.

Adjust the fuel curve. ''computer chip!'' You probably gained 10 to 15 horsepower from stock with current set-up. See if there is Dyno testing in your area for more accurate horsepower rating.

l have done many such things that u have tried on ur car & using a G-tech Tesla & a cam-corder to log the HP curv, l have come up with far less real world HP gain than what was advertised. for a total of only 12HP & about 500 dollars down the tube.
My experience with engines of all kinds has come to one final all encompassing answer to ur Question. There is the High dollar way & the relatively easy/ cheap way.
Port the heads, intake, exhaust, (just to keep things looking stock, bigger cam & a re-programmed ECU. Then maybee a compressor of some type blower or turbo (Lots a work or big bucks)
then there is the displacment game. BIGGER MOTOR

OR:
two steps colder spark plugs, a bigger fuel pump & a two stage NOS system with a 30-50/ & maybe a 75-100 HP split. Make sure that it is a wet system (injects fuel & NOS)
Remember that Horsepower & torque is always the same no matter how u get it & with less than 700$ & about 1 day worth of work its hard to beat. You dont use the extra thump all the time so the bottom end wont launch as soon as with a pump.
“ Has ur blower been beat, by the guy up the street, with nitrous under his seat?”
(Unknown author 1985 ish)
A 45/75 split makes my 96 sable GS with 160,000 a lot more fun than the stock 145hp
MAKE SURE that u dont start dumping nos under 3000rpm & dont get to silly with how much u use. after the first time l used nitrous.... it was the most fun engine mod l ever made!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

get a turbo or super charger,. or nitrous. both cost big $$$ and make it a lot faster.