Jerking sensation when automatic transmission is shifting gears and downshifting

There are a few possible reasons your 2006 Nissan Frontier might have trouble downshifting. Here are some common issues to consider:

1. Transmission fluid level and condition: Check your transmission fluid to ensure that it is at the proper level and doesn't appear old or dirty. Low or deteriorated fluid can result in poor shifting performance.

2. Transmission control module: The transmission control module (TCM) controls the shifting of your automatic transmission. If there's a problem with the TCM, it could fail to send the signal to downshift. Diagnosing a problem with the TCM typically requires professional diagnostic equipment.

3. Shift solenoids: Shift solenoids are responsible for regulating the flow of transmission fluid and controlling when the transmission shifts gears. A problem with one or more shift solenoids could prevent your transmission from downshifting. Replacing a faulty solenoid typically requires removing the transmission pan.

'Passing gear' is a term that means the transmission is down-shifted to a lower gear (e.g., from 5th gear to 4th gear) for improved acceleration to pass another vehicle. There is no physical component called a passing gear in the transmission.
To engage the 'passing gear' with an automatic transmission should require nothing more than pressing the accelerator pedal down firmly. The transmission should downshift automatically to the next lower gear (sometimes it will downshift two gear ratios, depending on your speed and how far you depress the accelerator pedal).

CK TRANSMISSION FLUID

run fault codes and look for faulty transmission control module. Check that all the connections are clean /tight and dry

was the oil clean of residue ?
you might have a faulty valve that makes the shifts rough

Hello
The Engine and Automatic Transmission (not applicable to manual transmissions) in this vehicles drive train are fully electronically controlled by a computer called the PCM and TCM (Power Train Control Module, Transmission Control Module). When a problem like this or other drive-ability related problems occurs the computer stores a record of the problem (there are of course some exceptions to this, like the fuel pump, engine coolant temperature sensor and MAF sensor for instance) in the form of a fault code in its memory, to read these fault codes you must have the systems memory scanned with a special tool. Once the fault code(s) are read you then must perform the appropriate diagnostic testing to find and resolve the problem(s) DO NOT REPLACE ANY PARTS UNTIL A TRAINED TECHNICAIN HAS DIAGNOSED THE PROBLEM TO AVOID SPENDING YOUR HARD EARNED MONEY ON PARTS THAT MAY NOT CORRECT THE PROBLEM. Also always check fuel pressure for correct spec for your make and engine type.

First thing ... pull the dipstick and check the oil. It should be bright pink or red, if it's brown or black and smells bad your oil has never been changed. Drain as much as you can, measure how much came out and replace it with synthetic compatible oil. Start the car and let is run for a few minutes and shift the gears a few times ... then take it for about a 10 mile ride to circulate the oil, stop and go now and then so it will shift through all the gears. You could also add about half a quart of Lucas Transmission Fix.

Most likely the second gear section of the transmission has gone bad. There are 3 or 4 different gear sections or assemblies in an automatic transmission, when they go bad, they go bad.

This is a hard question to answer without more information. If the vehicle has a sensation of slipping it is usally the automatic transmission that is at fault and it probably has to be rebuilt. The sensation of power loss could be from the slipping transmission. Try manually downshifting the trans. to a lower gear when going up a hill and see what happens. That can tell you if the problem is the trans, or the engine,

Cheapest thing to try is a fluid flush and filter change. Unfortunately, if that does not work, then next bet is probably a rebuild.