97 Bonneville SE 3800. 265,000 KMS
New air and fuel filters.
Car will run fine up to 150km hr if you gradually throttle it there.
If you go wide open at any speed engine starts to surge at about 4000 rpm right up to 5500
Surging stops if I back off throttle a littleand then speed will increase.
Have not pulled plugs yet but will put in a set of AC platinums on the weekend.
Any sugestions on what else may be amiss?

Thanks
Martin

A full tuneup does seem in order. While doing that, with the engine running, check all your vacuum lines for leaks.

Moved to 92-97 section for better visibility.