New timing but will barely get up to speed

Did one of the cam shafts rotate out of position when you took the timing belt off? This is very common and all you have to do is turn it back to the correct position, but you must turn it in the opposite direction that it moved. Usually it will turn clockwise. If it rotated clockwise then you have to turn it BACKWARDS (counter clockwise) to it's correct position. If you turned it forwards (clockwise) instead then the valve timing on that camshaft will be out by 180 degrees and it's not going to run right. Likewise, if it rotated out of position in the other direction you would have to follow the reverse procedure and turn it clockwise.

So recap. If it turned to the right, turn it back to the left. If it turned to the left, turn it back to the right.

In addition to the above, since the belt broke it is entirely possible that one of the cam shafts had an extra rotation with the same result as stated above. It is easy to assume that because all of the marks line, the timing is correct, but the only way to really tell for sure that I know of is to take the valve covers off and check the valve positions as you rotate the crankshaft manually.

Another possibility is that the new belt was not tensioned correctly and has jumped a tooth or two, throwing the timing out, though my money is on one of the camshafts being 180 off. It would mean that you are basically running on 3 cylinders. I wouldn't run it until you check it out. If you get detonation at the wrong time you could do some major damage.