400 miles per tank what could be wrong with my vw

I have a 00 jetta tdi, with roof racks and 17 rims. i recently changed air intake, egr housing, with new clean ones. also changed fuel filter, air filter. i am getting about 400 miles per tank i was much happier when i was at around 515 miles per tank.
any thoughts could my cat be clogged?

the car is all stock engine. only mods are sport suspension and 17 rims. i have had the car since new it has 140k on it. pulls strong just big loss of mileage. some smoke under load and high RPMS

I will preface my response by saying that I am new to TDis, and wouldn't consider myself knowledgeable enough to offer really sound advice. So, take this with a grain of salt.

Oh, I should mention though, that I consider myself a hypermiler. I have always gotten great FE with my cars, so in that regard I may be qualified to answer this question.

Anyways, the two things that glare at me are your 17" rims (14" are standard) and your roof racks. These are both HUGE killers of FE, and these alone could be the culprits of your bad mileage. When did you install them? Was it before or after the FE loss? Another thing to keep in mind is that mileage and odometer readings will be off when you switch tire/rim sizes.

Have you switched to a different oil lately? That could also contribute to positive or negative FE changes.

If you have a roof rack, 17 inch rims, an auto trans and you aren't venting the tank 400 miles is about right.

no switches bought the racks and the rims the day i bought the car with zero miles so it is not that. though i concur and they are the reason i was getting only 515 before but i was willing to sacrifce those MPg's i do not bother driving for high MPG's I just like diesel torque etc. this a out of the blue issue

thanks for the comment

Since you used to get better mileage you might want to check the timing, air filter, fuel filter and see if the intake is clogged.

I have a 5 speed and have had the racks and rims since new. always had much higher mileage than this anything above 475 is fine with me 400 makes me think something is wrong with the car.

i replaced all items IM, Egr housing, all filters only item was the pcv vavle was not replaced not sure what the item does.