Brushless Savage, Q's

i only lasts 5minutes with my 3800mah i thot i did around 8min but yesterday i only made 5minutes..on a newly charged batts my sav flips real bad i broke my rollbar..anyway i wish i have lipo i heard on lipo u get longer run time without reducing power?is that true?coz on nimh u can tell when youre batts are losin juice when my truck is not doin wheelies and becomes slower ..

The 8XL only lasts 5-8 minutes on 3800 mah? thats not very good, also what is the top speed?