When I hit about 50-60 KM/h, there is a noticeable chugging sound and light vibration feeling. To stop the chugging, you can either give it a significant dose of gas, or let off the gas a bit then reapply normally. Any ideas what this is?

Engine is a 2.5L FI.

It may just be due for a tune up, it's been almost a year I think.