[gear jammer 91"]

It could be over active abs. The abs on these early trucks only works on the rear axle, and could cause a peddle "shake" that would get worse the harder you hit the brakes. If the abs light is on on the dash this is probably not the case, I don't think the light turns on until there is a problem in the abs system and it is not functional. To check and see if it is in fact your abs you need to open your glove box, pop the top of the glove box out of the dash so that it will fall all the way forward and give you access to the area behind it. Behind your glove box is a black box with a big plug in it, this box controls your abs. If you pull the plug out of this box it will disable your abs, hopefully gettin rid of your problem. Lots of guys with first gens do this. Mine has been disabled for thousands of miles, some while towing with no issues. Good luck, hopefully that will fix it.

 

[gear jammer 91"]

The abs never worked on my truck so I'm not sure what it would feel like through the pedal. The only working abs I've had was on a rig with 4 wheel abs.