Flutter/Sputter can't tell when given more than 1/4 throttle

[Agent432]

I've got a 98' GTP and lately I've been running into the issue of when I give it about more than 1/4 or 1/3 of throttle the engine goes but starts to flutter or sputter but when I ease below that it's fine. Can sort of feel it pulling weird but below that much throttle the response seems fine. It's sort of hard to describe. Thanks in advance!

[Green97GTP]

plug wires, plugs, fuel filter, id check them first.