268 Voodoo cam rpm and vacuum

24 , has me wondering if I have a problem with 15 with a Comp XE 262 , 10 " difference is a big gap considering my cam is about the same .

They are nowhere near the same. You aren't even comparing apples to oranges here. The stock 340 cam has a much slower opening and closing rate, plus it's on a 114 center. Modern cam grinds have much more area under the curve and will have less vacuum.