Im New But I Need Help 91 Chevy Suburban R2500

hi ive been having problems with my 1991 Chevy Suburban R2500 for the past 2yrs and i needed some insight. now by no means i know my way around a car actually it was hand me down from my parents i got in 04 it was a daily driver on and off but i started driving it heavy in 05 runs good and everything until march of 2006 my car all the sudden started to shift funny and the speedometer will start jumping up and down all over the place and the parking light brake will turn on. i took it to aamco transmissions where the guy told me it needed a speed senor and a wiring harness it fixed it temporary and then it started to do the same thing and they told me it was the speed sensor replaced that again then it still gave me problems until the point i sat it in the driveway and drove another car.


well some months had passed and i decided to take it to my local chevy dealership and they told me the transmission was gone and i needed a new one but the price they gave me was too high so i took it to another place called mr transmission and got it rebulit(480le feburary of 07) and it worked fine and better than before until i took a trip to orlando the following 2 months after andw right when i got there the parking light brake comes on but no funny shifting and i kinda ignored it :great: but took note of it. so its working fine for 4 months no other lights or speedometers jumping up and down until the middle of august it went back to doing the same thing not being able to shift,speedometer jumping up and down parking brake light the whole shabang. i take it back up to mr transmission and they tell me that its a electrical problem and the transmission is fine and they dont have the proper equipment to diagnois it :no: and gives me a recommendation to a guy that specialize in electric in gm cars(former mechanic and everything ) but he wants 75 hr and that dont even go towards repairs to find out but im a college student with no job so i couldn't afford that at the moment so i had to let my car sit again for 4 months :grrrrrr:. some in december i got up the money to get my car fixed but never the less i took it back to aamco (dont ask me why) and they looked at my car again. come to find out they say i need a new computer and on top of in the middle of there diagnois my car wouldnt start because the computer was bad so i got the computer replaced(aamco wanted 650 but i got it for around 410 installed at another placearty and the car did give me any problems for a good month. then i come across the same problem again(a month ago) they told me i needed new wires going from the speed senor and some other wire i forgot which that went to the transmission because they were frayed behind my dash. i get that replaced and it works fine for a month until 3 weeks ago started giving me the same problems. now im back at i dont even know the number of visit and i leave it up there for a week and they tell me its not doing what i said it was and its driving perfectly well and i was like fine ill take it back when it starts acting up because now thats my only means of transportation.before i left the mechanic told me to take it up there when it acts up and don't turn it off(this was last week). now they are saying they are thinking its something called a drag modulator something that turns the mechanical signal to a digital signal in the speedometer and they are going to test it today and they will know. my question is am I getting the run around because i dont know next to little about cars/they just dont know what they are doing? should i bite the bullet and take it back to the gm dealership and have them tell me whats wrong with it. and plus i was trying to get the opinion of a gearhead on this site to give me idea of what they think whats wrong with the car. but if you have any reputable mechanics/electic specialist in the jacksonville florida area it would be highly appreciated. and excuse my grammar im tired and its 6:33 and the A.M as i typed this. thanks