1999 P71 w/poor horse power

[CrownVicInterceptor]

I have 1999 P71 with poor horse power, recently I replaced the factory cats, O2 sensors, mufflers and air intake system with Walker cats, Bosch o2 sensors, super 40''s and a K&N air intake kit.

Would a mass air flow sensor be faulty or a PCV valve, causing loss of horse power, would the check engine light come on, being it''s an electrical unit?

Also, around 30 - 50 when I'm driving at a steady speed the car does this little uh every few seconds...? Almost like trying start car with a dead battery.

How can I pin point the problem?

What other improvements can I make?

(Currently the check engine light is not on.)

[DtownInterceptor]

i had an issue like that with my p71 when i was on a trip back up north. could be as simple as needing to change ur spark plugs, i bought an old police cruiser and they had just used hodge podged spark plugs with different gap sizes...screwed things up a bit...or if you're unlucky replacing your coil packs which can be a bit pricey. pcv valve can bet tested to see if it's good or bad but like spark plugs that's something you should change at least every 30k. can't hurt to replace either of those