Vauxhall Vectra. A tooth out?

Hi there! I have just recently replaced head gasket on a Vectra 1.8 16v on an R plate. Since I went to start it, EML came on and it took ages before it would start. I have rotated the engine so all the tming marks are in line. The belt is tight. It is not missfiring. Whwn the engine is going round it hesitates for half a second when you rev engine. I had it hooked up to diagnostics and description "rpm speed signal" came up. Tested cam and crank sensor and everfything is all good. What next