MV6 various problems

Hello, I have a few problems with my Omega B MV6 Caravan Automatik 134tkm Bj.95, which would be there: – The MKL always goes to as soon as I give no more gas, no matter whether country road or city trip, it goes out again and again but sometimes it takes a longer time 3-4 minutes. – Sometimes the speeds are most noticeable when I drive through a 30s zone. and now the worst when I refuel the Omega I can drive ONLY 490KM what I find very little is or is the V6 drinking so much? I hope someone can help me, I haven’t had the error memory read out yet. Thank you very much in advance.