When I drive slow or faster than 80K my gear stays on Gear one (I have automatic gear) and I am getting a loud noise from my engine and I tooked to a repair shop by he said he can't do it only Chrysler. Also I smells gasoline everytime I drive my Van (1996 Town & Chrysler)

The only way to diagnose is electronically by asking an auto electrician to scan it with a pro grade scan tool computer. They can also record what is happening on a drive! It sounds a mess for sure, mechanical and electrical and the computer can diagnose both.

https://www.google.com/search?q=mobile+auto+electrician+near+me

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I would say some gear teeth are missing or the bearings are worn, this particular model did suffer gear box troubles, Molyslip Gear Oil treatment will help.

As with all unusable vehicle noise complaints it is important that the noise be listened to first hand, so have a shop test drive this with you on board to point out the noise to them when you hear it start in your vehicle

I've just bought a K13 Nissan Micra and it doesn't sound quite right. The noise I hear also seems to be coming from the back but it sounds like when you chop down a gear in a manual going down a hill and the engine revvs, well this is the noise I get in the automatic speeding up and slowing down, even just cruising at a steady speed. Any ideas people? Apart from this noise I love this car.

Might be a modual needs replacement

Trans range sensor on the transmission!!

well, without hearing the noise myself, i could guess that the torque converter clutch might be going bad. the torque converter is the part that transfers the power from the engine to the transmission via viscous fluid motion, the converter also has a clutch that internally provides a direct connection inside the converter for better fuel economy. but as with anything labeled as a clutch, it wears down to a point where is slips. the noise your hear could be the torque converter clutch slipping. i owned a 90 astro van with the same drivetrain that made a noise similar to what you speak of up hills. while driving up hills, fully depress the accelerator and if the clunking noise occurs, then the whine goes away as you accelerate faster in a lower gear, very likely this is the case. you would have to have a transmission shop diagnose further. i drove that old van for five more years cause i didn't want to pay to have transmission repaired. it can be very expensive.

could be a gear box fult maybe its the first cluch in the box slipping on an autobox?

What do you mean by loud... Loud where??? If noise is from engine, make sure that the mechanical fan clutch is not "locked" (it's supposed to freewheel when cold... if it does not, it will "roar" when driving.