I have a 91 4runner 3.0 5 speed 4x4. Lately I've been having this problem and its been getting gradually worse and worse. When I hit certain speeds, usually around 45 mph, my truck will suddenly start shaking really bad like I'm driving over something really bumpy or that bucking feeling you get when your about to stall. Lately this problem has been getting worse and worse. Another problem I've had is while during acceleration. Sometimes when I take off from a start my truck will stop accelerating as I push the gas pedal down more, then suddenly, the power will cut back in and I will feel the motor start pulling again. This is all while I press the gas pedal slow and steady. Any ideas what the problems could be?

 

did you check the intake, 3.0's are notorious for loosing a vast majority of there power from just a simple air hose leak.

 

try checking you coil, and plugs, its ussually something simple as a normal tuneup.

 

mine had the exact same problem!!! i remedied it somehow when i fixed the stuck valve, put the N&N in, changed the spark plugs, wires, cap, rotor, and switched over to Royal Purple... it just randomly disappeared...
check the next time it does that, all your dummy lights should flash on your gauges... or at least the CEL...

 

check for any loose grounds
check for any trouble codes particularly if the CEL comes on when it happens

 

da... i agree, check the cel... i never did because i didnt know about this wonderful website at the time, and now i wish i did so i know what the heck was happening...

and correct me if im wrong, but it is possible to pull a code even if it doesnt throw a light, right??

 

yes, you can check codes even if the light isn't lit.
just short the appropriate connectors and turn the key on and the CEL will blink if there are any stored codes, even if the condition has cleared.
post them if you have any.

 

I don't have a check engine light, but I will probably check it anyways to be sure. I gave it a tune up about a year ago, but now that you mention plugs and wires it feels like it did before I gave it a tune up, I will defiantly check all that out.

 

you have a check engine light, the previous owner might have pulled the bulb out of the dash. But it looks like and outline of an engine, and IIRC, it lights up orange/red color

 

Those codes won't tell you much but check em anyway and let us know.
Bigblock

 

I have an actual check engine light, what I meant to say is that it is not illuminated. I haven't checked the ignition system yet but I noticed that my from control arm bushings are absolutely SHOT. Also, I have mismatched tires which could possibly contribute to the shuddering, and my diff is leaking.