Hi. I previously owned a 1990 4 cyl 4 Runner. Loved it till it finally gave up the ghost a year ago. It was rusted out and not worth the fix. I bought a 6 cyl because I thought it would have more power and better gas mileage. And I could keep my 4 cyl for any parts I might need Wow!!! Big mistake. I know they are underpowered and get bad gas mileage but I think mine is way below average. I get 8 mpg and have real low engine power. It slows down and struggles going up overpasses and small hills. When I try to pull away from stop signs it feels like it's going to stall. A real ***** when trying to get onto highways and beat the traffic. It take forever to get to speed. When I floor it it sound like I'm tearing up the road but I'm barley picking up speed.

This is the second engine in it. The head gasket blew 1 month after I bought the truck and the bottom end let go a month after replacing the head gasket. This new engine out of a parts truck I bought performs exactly like the first. So I'm thinking something else is making it run like that. I took off the headers that were on it and installed factory manifolds and a new exhaust system 2 1/4" pipe and no change. I upgraded the spark plugs and cables. Changed the O2 sensor and fuel filter. No change. Threw on a K&N air filter and took it into the guys at Toyota to run diagnostics on it and they tell me that they can't find anything wrong. Come on!! Anyone out there know of any mods, chip or software upgrades to give this thing some realistic power?

No, I think to dump money in the 3.0 is a waste the engine puts out like 155/190 in a 5K lb running 31's you can't expect much.

8MPG is silly though I get about 16-18mpg with 128K, are your plugs gapped right.
IIRC 0.031

The TPS sensor could be your problem.

Don't get me wrong they are slow and maybe that's just it....but the 8MPG makes me wonder.

To be honest I will drive mine untill it dies but when it does I am going to swap the 3.4L into it more HP/TQ and you can put a TRD supercharger on it.