96 silverado, lots of problems

I've been reading through these posts looking for help, so i decided to just post my own. you guys all seem like pro's, hopefully you can help.
I recently bought a used Chevy Silverado. it's a 94, v8 5.7L, over 166 thousand miles and it has multiple problems, i love trucks and this but was all I could afford. here goes:
+Spedometer and odometer stopped working while towing a boat, boat is approximately 5,500 lbs. gages still don't work, both read highest settings(55k rpms and 85 mph) and never move.
+Brakes don't work quite right, almost put my foot through the floor to stop. pressure feels very low, pumping them makes them very firm but only for a short time. replaced master cylinder and rear brake cylinders and nothing helped.
+REALLY weird problem with rear taillights. they don't come on when i hit the switch to turn them on, but when the switch is on and i hit the brakes, brake lights come on and taillights come on. when i take my foot off the brakes the taillights get very dim, and everytime i depress the brake pedal after that all the rear lights go out??????
+wiper moter was burnt out, replaced it but now it also does not work properly. only works at highest speed and turns on wiper fluid jets. had to just disconnect the wires to the wiper fluid container.
+while at idle or while moving at any speed it feels like my truck jerks/rumbles, whole list of possabilities. exhaust, fuel injector, bad transmission fluid, etc. the longer i drive, the worse it gets.
+my AC is weak and smells like vanilla? please, for the love of God, help.

You definatley got some issues. I would start by getting a chassis wiring diagram and a ohmmeter.And buy some rebuilt calipers for front brakes. You can get them complete w/ pads for about $38 ea. with core trade-in, they call them loaded rebuilt calipers.You should check your grounding. Where to start? you name it, you have problems evrywhere.

I believe in these trucks the emergency flasher switch made the lights act funny, try disconnecting it and see what happens

You said, "+my AC is weak and smells like vanilla?". Well from my own experience is that if you are smelling this, try smelling it at your tail pipe as well. In either case this is a strong sign that you gaskets on your heads or you heads themselves may have developed a crack. This will let coolent into the exhaust chamber and with the exhaust being so hot it immediately evaporates the liquid and some how its seeping into your ventalation. Please beware that these fumes are very dangerous to breath, if this is what it is. Also if you see a constant stream of white smoke from your tail pipe thats also a sure sign. I really hope you did not spen much on this truck because if you want to keep it with all the issues you have mentioned here you about to have some major repair bills. Good luck!

Myself, I just purchased a red Silverado '96 ext cab. And sofar I have only had to replace the windshield and passenger mirror. I fully expect to have to poor money into the unit in the (hopefully) years to come.