just flew matt chap 40 with th 75 motor flys good
but with any more than 3/8 inch up elevator it snap rolls right baddddd
any ideas why or how to fix?

Sounds to me like a combination of 4 things:

1- Tail heavy
2- Tail heavy
3- Maybe one elevator half moves a bit more than the other

and

4- TAIL Heavy

Too much elevator, too much speed, too much weight (wing loading)

here's 3 chances out of 4 it's tail heavy.

The Matt Chapman CAP, according to the specs on Tower, only has a 562 sq in wing area. With a .75 in it, it is going to up near their advertised max weight of 7.5 lbs. At that weight, your wing loading is going to be 30-31 oz/sq ft. This is pretty high and will make the plane snappy under any conditions. With a tapered wing and thin airfoil, it doesn't surprise me that it snaps easily.

Get an accurate weight on your plane and calculate your wing loading (lbs/sq in x 2304). If it is over 30 you'll have to fly accordingly.

Here are a couple of more things to check:
Are your ailerons drooped. They should be level with the airfoil or maybe, slightly up. This will act as a little wash out.
Stand 10' or so out in front of your plane with it on a table and slowly squat down checking the top of the wing. You can tell if one tip is higher than the other, meaning you have a slight warp. The lower tip will stall first.

Once you nail down the cause of the problem, you can start to fix it.

the snap is a result of a high speed stall induced by the application of too much elevater.cut back the elevater throw.

You know, I had that problem with an US 1000 and all told me to cut back on the elevator throw. The problem was that I did not want to do that. Now it still may be a balance problem, but my solution, THAT WORKS, is to mix the ailerons to the elevator. Up elevator and down ailerons. The more you droop them the tighter the loops without stall.
MAKE SURE YOU CAN TURN OFF this mix!!! If any head wind at all, you will ballon bad upon landing. No wind and the plane lands slower.
You will also need to turn off for good flat spins.
My two cents.......note, have three planes with twin engines, max elevator and this mix.
Twinman