Suzuki Jimny 2005 automatic powerless on highway

Hi I have a problem with my jimny 2005 automatic but can not find what the problem is. The car feels really nice in the engine and automatic transmission. But when you drive at higher speeds on a motorway for example and there is a slightly steeper road it loses speed and feels powerless. Is there anyone else with a  automatic Jimny who can share their opinions? Does not reach more than 100 km / h on the motorway and as soon as there is a little hill the speed is reduced to 70-80. The car is in very good condition otherwise with service done and I also changed the oil and filter in the gearbox. but it did'nt help. No codes. It have 96.000km. Please let me know your opinions guys its my first Jimny and i love it but i need to fix this problem. 

Welcome to the forum. I only upgraded to automatic about 6 months ago so am still learning but it definitely shouldn't be that slow on a motorway. Mine is quite capable of holding speed on fairly serious inclined sections though it will change down on the most dramatic hills much like I had to with the manual before it. As to why, it could be a few things, you said you have no codes, have you the facility to monitor live data from the gearbox with your diagnostic equipment? SZ viewer allows you to see real-time parameters like torque converter slip and shaft speeds etc which can help determine what is going on. The automatic usually seems to be quite robust if looked after.

It's probably not the automatic gearbox unless the car has entered 'limp mode' if the Jimny has one?

Has it always been like this or has just started?

More likely it is air/fuel/ignition/exhaust which is causing the lack of performance.

Air - Check air filter & MAF sensor
Fuel - Correct fuel, check filter, O2 sensors
Ignition - Check plugs, coils (crack), timing
Exhaust - Is the exhaust or CAT blocked
Brakes binding?

As it won't rev it suggest air/fuel flow problems, I would start with the easy things, air filter, plugs and work you way round to the difficult things. The plug colour might tell you more about waht is going on.

As Lambert says does your code reader give you live values, that might help.

Unfortunately without any codes logged, it might be a case of working your way through the list. I am having a similar problem (not as severe as yours) with my other car (not a Jimny), it's just a case of checking everything, I have been through O2 sensors, coils and plugs, air filter, now it is looking like an over-reading MAF.

Maybe we should start with which Jimny, and what engine does it have?

Thank you and thanks for your information. I dont have the diagnostic to see live data from the transmission. I maybe should go to suzuki and let them search for the problem. It goes up to 4000rpm and no more then its stop with power and when its shifts to the last gear it looses more power in the 90km/h. The gearbox shifts smooth and nice. The airfilter is new, the exhaust and cat is new, spark plugs is new. The only thing i dont know about is the fuel filter. Its a Jimny 2005 vvt automatic i think its the M13A with 16v DOCH enginge. 

It only revs to 4000? It should rev to 6000 cleanly and it will change gear up there too if you leave your foot on the floor. First easiest thing to do is check that there isn't excessive slack in your throttle cable as this will affect the cars ability to rev and also the change point of the gearbox. It's easy enough to adjust but don't over do it or it will affect the idle. A Bluetooth obd2 tool will be around 15 pounds on amazon, I have a veepeak vp11 and I now use SZ viewer free off play store as recommended by this forum, it allows me live reading on all available systems and is very useful.