The tachometer kind of jumps around, always drops then goes back up i dont even know if its right.

https://www.toyotanation.com/threads/2007-tachometer-help.427576/
https://www.ifixit.com/Answers/View/97565/Why+is+it+when+driving+the+RPM+gauge+drops+or+jumps+up
https://www.yourmechanic.com/article/3-essential-things-to-know-about-your-car-s-tachometer
https://www.toyota-4runner.org/4th-gen-t4rs/118458-tachometer-reading-low.html
https://www.youtube.com/watch?v=eLYPENYhy28
https://www.youtube.com/watch?v=jpObqMse2CY
http://www.fixya.com/cars/t17264530-tachometer_rav_4_not_working

Sounds like the sending unit has an intermittent short to ground. Unhook the the wire from the sending unit, and see if the needle stops jumping around. If it quits jumping around, replace the sending unit. If it still jumps around, you have a bare spot somewhere on the wire and it is hitting ground which will cause the needle to jump. Cut out the bad part of the wire and splice in a new section. That should fix it.

Sounds like the tach is either bad and should be replaced or there is a short or loose connection to or from it. Check the wires in and out of it. If it's in the dash, though, it won't be easy to get to. Good luck.

Check that the sensor that feeds info the tack is good.

I would get ride of it

No reason to even discuss all the possible issues

The trans sounds as though it is slipping

Not worth putting any money into,not at the kind of
mileage your putting on

Your better to lease a new one

I dont think your problem is related to the intake manifold gasket.My experiance leads me to believe that your speed sensor is bad(VSS) Back in the day it was a cable attached to the tranny that gave you mph on your dash.In today's "fly by wire" society this would be the most likely suspect.symtoms would include downshifting for no reason your speedometer would drop to 0 and the tach would skyrocket.Vehicle may come right out of it and operate normally,or it may continue to buck for a while and then even out.I would start there.

check to see if your firing order is correct

Sounds like the ignition switched circuits are not always powering up.
I suspect the ignition switch itself, however, it could be relays in the system.
I would start by measuring the voltage drop across the ignition switch, if more than 10% anywhere I would replace the igintion switch (under dash).

What kind of a rip off is this? We can help fix your problem for free, but if you really want a solution you're going to have to ante up $10 plus. And, by the way, if you fixed it without our help, how about telling us how you did it so that we can charge the next unfortunate soul with the same problem for the information you have provided us free of charge. Really, FixYa, THANKS FOR THE HELP.

Suggest that you look for the ground wire of the tachometer gauge. It maybe disconnected. Or else the gauge itself is destroyed.