96 merc marquis bogging off idle

Moms old car she kept it well, ran great for a bit then died/slowed up hills a few times, now bogging off a stop to start. Runs crappy when cold

88k miles, plan on starting with plugs and new gas filter.

1) do I need the platinum plugs?

2) tool to change gas filter?

What else might I track down to the bogging? Have tried iso-dry gas and FI cleaner.

Some more background. I have worked on engines all my life. Started with lawn mowers-minibikes, motorcycles at a dealership for a while, cars, trucks, tractors. Have a dozen Stihl saws most of which I got free/rebuilt. Built 500 HP small block motors from bare block. Have not wrenched on new stuff. I love a 4150 Holley, carter mech fuel pump, and 100LL gas.

It's the newer stuff I'm still ignorant on. I can rebuild a front end or motor, the newer FI stuff is all new to me. Hell until I worked on this car never seen the "new"clamps on the fuel filter, E-Brake on rear 4-disc, etc....

But I have tools and can be educated. Maybe I can help someone with a 62 or 67 williys, 39 9N, 72 2000 3-cyl gasser?