slow starting on fully built drag car

Hey guys my dad is having issues with his 1980 mustang. He asked if I could help him out by asking on stangnet since i'm always looking around on here. The problem is that his car starts easily when cold but once its warmed up and you try starting it again. It acts as if the battery is weak and turns over slowly. Its charging and holding a charge. Its got a brand new 429 stroker windsor motor with all pre fitted parts from the machine shop. Last year it had a 408 stroker motor and did the same exact thing. We have a high torque mini starter all parts on this car are new and high quality parts. Any ideas thrown out would be greatly appreciated. I'm not expecting anyone to spill there guts out just suggestions or ideas. thank you

p.s. we want to race this car and win some races
 
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