Intermittent miss/surging after timing belt replacement.

I'll describe exactly how I timed the valve train. Before I removed the old belt I send the no. 1 cyl to TDC. When it came time to put the new belt I positioned the cam gear UP arrow up and positioned the two timing hash marks exactly parallel to the plastic rear cover. I then set the crank gear mark exactly on the dot on the oil pump housing. I put the belt on then aligned the timing mark on the balance shaft with the mark on the oil pump housing. I set the oil pump timing mark to twelve o'clock. I carefully put the balance shaft belt in without disturbing the balance shaft. I then released the tensioner so I can apply tension to the belts, and rechecked the timing on the cam and crank (exact). To verify the valve timing I put the crank bolt in and removed the spark plugs. I rotated the engine through a full cycle and set it to TDC no. 1 cyl, and rechecked the valve timing. Once again exactly correct. So I put everything back together and drove it and had the symptom I described earlier.

So. I took it all apart again all the way down to the timing belt, and checked the valve timing, and low and behold it is exactly correct. One tooth in either direction would have mis-aligned the marks. At this point I cannot get the timing any more exact than it currently is.

Are there any other suggestions?

Thanks.