Thanks for the link, google wasn't being my friend with a quick search on the matter.
I'll have to review it a bit closer, but one common mistake stands out:
When you reduce government spending, GDP will contract, because part of the GDP equation is government spending/debt. When this shrinks, so does the GDP. Also, a fair amount of the income gained through taxes comes from federal employees that will be terminated under this plan, which also decreases the amount. I see he accounted for a fairly small decrease in income to the government, but whether this was calculated based upon how much is actually cut, the decrease in tax rates, or just being conservative I'm not certain at a glance.
In any case, that makes the GDP related charts practically impossible to gauge, as the exact impact will be very hard to determine, though you can get in the ballpark based upon what and how much cuts occur.
I'll dig into it a bit deeper later, and see if maybe the answer lies in the numbers somewhere.