My audi a4 b6 2001 model.automatic. the problem with 1st gear.very slow taking off.

It is in "limp" mode which limits the transmission to only 3rd gear. The transmission fluid level needs to be checked and the "basic settings" need to be reset in the Transmission Control Module.

You can not change transmission fluid in a
trans that already slips

It will slip worse

Now you to have it replaced or rebuild it

Have no idea, as i guess you don't either,
about the clutch,flywheel,gearbox,your thinking
about a standard shift

check oil level in gearbox, if auto check fault memory, will go into emergency mode and stay in 3rd if there is a fault. gear position display will all light up.

down the dipstick tube!!!(really)DO NOT OVERFILL...
Your audi is fitted with a fuzzy logic gearbox, it will change according to your driving style.TRY THIS,put into 1st and without touching gas pedal, let the car accelerate to top gear,stop Then using onle 1/3rd gas pedal do it again.then using 2/3rds do it again.then only using the minimum pedal req accelerate to max legal limit.(try not to use brake pedal,let the car slow down itself,until you have to)then drive as normal, it will feel like a different car.

sound like 1st gear might be slipping or stripped

Did you change the transmission filter? Sounds like no Front pump pressure. dirty filter will cause cavitation of the pump and damage to pump. Damage to cutch packs will occur too. Do not run until investigating filter, make sure o ring or grommet in valve body is present for filter

you may not need a transmission replacement, just try replacing the sensor of the transmission, it may help

Silly question: Have you checked the transmission fluid level, and is it to manufacturer's spec?

Not overly familiar with Audis but it sounds like either a.) you have an electronic tranny that has a serious bug or b.) there's a problem in the computer of the car itself. What is sounds like is the car is taking a long time to "understand" that you're telling it to move forward. How new is the car? When you push on the gas before the three minutes, what happens?

I think your transmission is faulty.