Engine performance

2005 KIA Sorento 4x4 Automatic V6, 3.5 L :
When I drive the suv on the highway 60 miles, it drives hard (loud) and feels goes with one gear. When I drive the suv on my house street 35/45 miles I get all the gears. No engine light...RPM's normal. I took it to a mechanic but they think I'm "crazy",they can't figure out what's wrong. What do you think is the problem?
Thank you,
Takis

At 60 mph, what is the engine rpm?

Does turning the OD off, result in any changes in the engine rpm?

Have you tried to retrieve for trouble codes?

Thanks for your fast respond...
I'm not sure about the engine RPM's.Feels like the OD is off but I'm not 100% sure.Somebody says it's a solenoids problem.But again,
No trouble codes.

If it is a solenoid fault, there should be trouble codes.

You need to monitor the engine rpm to be sure if the transmission is in OD.

I will,thanks.
Now if it is the solenoid fault ,the engine light has to be on ?(or just trouble code?)

Engine Light might not come on but codes could be stored. Most pasrts stores provides free scanning services.

ok...
No trouble codes.RPM's are normal,I think. When I was driving 30-40 miles,the rpm's was 1000-2000/when I was driving 60 miles was around 3000 .Very frustrated...Thank you!

I took it to another mechanic today.He says he thinks is the rear differential(85%) or the transfer case(15%).What do you think?
Thank you,
Takis

I believe it is roaring noises that you are hearing and nothing to do with the transmission or engine and these could be from the rear differentials, transfer case, tires or wheel bearings.

When the noise appears, does releasing the throttle pressure affect the noise level? If yes, it should be drive train related meaning it could be from the differential or transfer gears. Have you checked the oil level in both components?

If releasing the throttle or cruising in neutral does not affect the noise level, you should be looking at the wheel bearings and tire conditions.

It is impossible to understand noises and provide recommendations online and the mechanic who did the test drive should be in a better position to make any recommendations.

I check yesterday if there is oil in the rear diff. or transfer case ...and there is.Like I said earlier one mechanic says he thinks 85% is the rear differential or 15% is the transfer case. Now ,my question is:If one of those make the noice ,can it cost the problem I have?In other wards can the suv drives "hard" and feel like it goes with one gear?
Also ,with a problem I have do you think most is the rear diff. or the transfer case?
Thank you very much for the fast responds.
Takis

What do you mean by driving hard? You mentioned the engine rpm seems correct with the gears so I am confused by what you are trying to describe.

1st question:2005 KIA Sorento 4x4 Automatic V6, 3.5 L :
When I drive the suv on the highway 60 miles, it drives hard (loud) and feels goes with one gear. When I drive the suv on my house street 35/45 miles I get all the gears. No engine light...RPM's normal. I took it to a mechanic but they think I'm "crazy",they can figure out what's wrong. What do you think is the problem?
(((((That's my 1st question))))
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I mean ...I hear "louder" noice than before and feel going with the same gear.
Thanks,
Takis

I did mention that if the noise is present at higher speed, it could be the wheel bearings, tires or transmission/transfer gear.

It is not possible for me to make any comments on which is causing it . The mechanic who did the test drive should be in a better position.