Q: car studders during acceleration only between 20-30mph

Hey, guys! I have a 2005 Audi A4 1.8T Convertible with 89K miles. I recently started driving it again after it sat in my garage for about three years - it’s my second car. It recently started vibrating between the speeds of ONLY 20 and 30 mph. Before and after those speeds, it drives great! Ive had a few thousand dollars worth of maintenance and repairs done in last few months to bring it back out of hibernation. I got oil change/filter, tune up with new plugs, timing belt/serpentine belt ,new engine mounts, new brakes and rotors, and tires rotated and balanced. There are no leaks or cracks in any belts. There is no smoke at all from exhaust. There is no whistling sound from Turbo. No check engine light. My neighborhood mechanic doesn't know why stutter. Audi mentioned I may need a new fuel pump because of "sludge buildup" but I have owned the car for 12 year always got timely synthetic oil changes/used premium fuel. Its sat in a garage for 3 years so I doubt it has "sludge"

My car has 89000 miles.
My car has an automatic transmission.