There is usually nothing more in that curb but more concrete.
If a person wanted to, they could just make some cuts.
Caution, this will be ugly, awful work.
What is tempting is to just lay a 2x6 across the front of the lip, and use that to mark off the portion to be removed.
Resist this temptation.
Instead, use a 2x to scribe the inside width of the truck tires. Then mark off 5-1/2" across.
You then need a cheap circular saw for which you have little attraction or history with; barring that, a cheap one from pawn shop or HF.
You want a masonry blade--not diamond--(I'd get 3-6 of the cheapest you can find, you re using them to destruction) to fit that saw.
Cut (this will be messy and awful) the marked lines as deep as the saw goes. if the saw does not die and/or you still have blades left, score within the to-be-removed area to make 1-2" slices.
Rent an electric "jack" hammer.
Start at the outside, and carefully us the wide blade on the hammer to knock 1-2" wide bits off.
Take small "bites" and check the depth as you go.
This will be a great deal of work for the 8-12" wide 5-5.5" long 3-3.5" deep cuts. This is where you will appreciate the not committing to knocking 5" off the whole 8-9' long edge.
If you are really OCD, you'll need to figure on some time in kneepads with a concrete chisel and a 4# hand sledge.
What a person could do, instead, would be to get a treated 2x about 8' long, and fasten it the to the garage floor about 6" past the lip, so that you have a stop after the stop. A bit of 2x8 or 2x10 tapered on a band saw could be tapcon-ed in front of the lip in the garage, too.
With "ramps" in place, I'd be inclined to make an "L" of 2 2x to use as a stop. That's me, though; others differ.