Throttle linkage:
First figure out if it is in the pedal to cross-shaft or cross shaft to valve cover to IP.

Open the hood. While standing (car does not need to be running) reach your right foot onto the throttle pedal and start pressing.
If you do not see movement of throttle linkage that corresponds to your foot then check the firewall for the bushing and check linkage there.
If you do see the linkage moving along with your foot pressure then concentrate
on the cross shaft, top of valve cover. These pieces have adjustments and are easy to set.

I seem to get some travel too, but I accelerate and reach top speed just fine.

Transmission: You should really have a hand held vacucm pump like a mighty-vac. You need to rule out any vacuum issues (easy to do).

Interior MB Tex: I doubt the kit on TV will help, it might work for the dashboard.
I went to a local upholstery shop and asked to have a small tear fixed, they were able to help.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
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03 Ninja 250