My advice to you is try another brand of lipo (nothing against hobbyking) but we have tested there turnigy packs on 1/10th scale and 1/8th scale and the voltage drop on scale is very rapid not linear whatsever .

There packs are just not cut out for racing .

Alot of the other brands like intellec ,he energy,pro amps,orion and so on had a voltage drop on first load but then levelled off and were linear for a period longer than 8 minutes before they dumped but the turnigy drop 2 minutes after its start up load .

so please try another lipo brand and you will see the difference dont forget 5.5T do demand lots of current and a stable current and voltage drop .

let me know how you go