2003 Audi A4 1.8t quattro acceleration problem

I have a 2003 Audi A4 1.8t quattro and ive had many problems with it since i
first got it but when i first got it it had the stock mufflers on  it and was rusted
very bad and my car was very hesitant and acted like it wasn't going as fast
as it should and would not pick up in speed until it reached 30 or above, so
therefore i got it straight piped and that never fixed the problem either. but
about 3 months ago i was driving using the tiptronic shifter and then placed it
back in drive and stopped at a red light. ( My car at this point was still started
and idling perfectly fine) but as soon as the light turned green i pressed on
the gas to go and it was like it went into limp mode or something and
wouldn't go but then started to give me a little bit of gas for me to get out of
peoples way and stopped. i turned it off then turned it back on and it started
fine and tried to rev it but it wouldn't do anything. I waited 10 minutes and
turned it back on and it started perfect and revved up perfect. then i tried to
drive it and it would lag a little but then drove perfect in Drive, Reverse, and
in tiptronic. but then once i stopped again it was not letting me accelerate but
was still started and idling. I got it towed and it sat for a while and once i
went to drive it it drove for a good 30 minutes then once i came to a
complete stop at another light it did it again. I waited 10 minutes and it
started and let me drive it for another mile and wouldn't go any further again.
then i repeated it twice to get as far as i could but the second time it just
wouldn't even start. Now recently i had a mechanic with the same car as me
but his was a VW. We fixed an exhaust leak and a dry rotted fuel line and
drove it and it drove perfect except of course for the hesitation it has. kept it
running let it sit but then drove it for about 30 minutes then turned it off and
let it sit for an hour then started it up perfect and idling perfect and drove
good for another 30 until i got to my neighborhood and went over a couple
speed bumps and when i got to my last speed bump i went to accelerate and
NOTHING. it wouldn't go it wouldn't reverse, it would let me use tiptronic.
everything on my dash just had PRND all bolded and not separately  bolded
when i would put it in gear. I really would like to not take it to audi because
they're to expensive and if someone could help me and could possibly know
a solution to this please because i really dont want to get rid of my car:(