AT&T U-verse → sporadic speed test?

ok heres deal, i have been a road runner person for past 10 years... i seen att has a great deal on internet so i take it.. i am on the turbo max deal with 24 down and 3 up,,, but the speed test are so sporadic i dont know what to believe.. if i go to att speed test site it is showing a strong up and down signal.. but speedtest.net is do sporadic i am confused.. it will hit 12 mbps in a fraction of a second and thats what it uses as my speeed? doesnt seem accurate.. hard to explain but most speed test sites are between 1 mbps and 16 mbps up and down!!! it is in no way consistant! is this normal for dsl or what? i am lost here.. when i was on cable the speed terst where all constant at 30 mbps.. and stayed there they didnt jump all over like this att uverse dsl.. any insight would be great!
thanks
steve

1) ATT.com speed test is highly inaccurate for most people.
2)Do you have U-verse TV? It uses up to about 6ish Mbps per HD TV running.
3) I know what you mean of the super fast speed tests. Once I refresh the page it goes away though.
4) Can you try »speedtest.verizon.com/fios300/ ?

i am getting 23 Mbps down and 3 M bps up... and that test seemed more accurate,,, it wasnt so sporadic.. it was solid and stayed the same the whole way through.. not at all like the others.. the others where up and down like crazy and some only lasted a secomd for the download.. would you consider that test accurate? because it is exactly what my speed are supposed to be....
one thing i have noticed since the switch from cable to dsl, is all websites seem to load faster... quite a bit snappier.. if that makes since!... i mean really web site load very snappy compared to cable?

I think the Verizon test is one of the more accurate tests out right now(For non cable at least). It's a newer version of Ookla's many different versions. It depends on the faster loads between each other thing:

1)You're just having it in your head
2) Your cable company had poor routing for your area or your connection was a little messy.