chevy man needs help in windy city

i have a 92 lumina apv a great van( has 253000) on it and was the best car i ever owned until.......this.last week end my girland i were coming back hrom ind.we stoped 4 coffie and took off.while driving i noticedthe van didnt accelerate right (nothen to bad but just enough for concern)well i got worst by the time i got to valporazo (50 miles) i had to floor it to get 15 or 20 miles pr hour out of it. i changed the cap and rotor no help. cut the cat off still the same i changed the o2 sensers10k ago new plugs and wires. i change the oil every 3k in this van please help i love this van and dont want to give up on it it has great oil persher and everything eles is fine. thanks for have this forem

At that kinda mileage, I would suspect the timing chain is jumping. Usually by 150,000 there is no teeth left on the top gear. Beyond that, you are living on borrowed time.

Most times when a chain slips, it does so from the rock-back that occurs when the motor is shut off. Explains the sudden onset after parking it. Will probably continue to jump, untill it is undriveable.