<!-- from fixya rte -->How do I Replace the gear shift - Yukon Denali GMC Cars & Trucks

I suspect that it will be in the shift mechanism
If it is a cable shift then replace the cable
If it levers or other linkages check and adjust or lubricate as required
I doubt it is in the clutch as you haven't mentioned difficulty in selecting first gear only shifting from 1 to 2nd.

find a tranny man,
any ASE shop works
ask em.' to CHeck it out.

is your chevy impala auto gear or manual? if auto shift I suggest to
replace the gear box or take to a professional auto gear mechanic,if it
is a manuel gear box all you have to do is replace brass cones your
problem will be solved

The governor likely failed. Not a difficult part to find or replace.

replace the gear shift and top section completely unless you can see what is broken or missing that will not allow the gear lever to move the shift rails.

The gear may be stripped, can't catch other gear,have you been grinding this gear,will have to go into transmission and replace third gear, will have to wind second gear out and shift to 4th gear.May be better and cheaper to get a remanufactured transmission cause all parts are new versus just 3rd gear being replaced.

The gear shift lever indicators tell you what gear you have an automatic transmission in on your vehicle. The shift solenoid tells the transmission when to shift gears and what gear to shift into. Newer model automatic transmissions have electronic shift solenoids that are activated and change gears based on the speed the vehicle is traveling. Troubleshooting either one of these transmission components is relatively easy if you know a little about automobile mechanics. With the right tools, you can determine whether the transmission shift solenoid is having a problem. Gear shift indicator problems can be determined simply by moving the gears into their designated position.
Transmission Shift Solenoid

• 1 Raise each corner of the vehicle up with the car jack and place jack stands under the frame. Make sure the car is raised high enough so you can work under the car freely.
  
• 2 Slide the drain pan under the transmission fluid drain plug. Remove the drain plug with a ratchet and socket, and let all the fluid drain out of the transmission. Remove the transmission pan bolts with a ratchet and socket. Pull the pan away from the bottom of the transmission, revealing the transmission shift solenoid.
  
• 3 Wipe off the shift solenoid with a shop towel. Disconnect one of the two plugs that attaches to the shift solenoid. Turn the knob on the volt meter to the ohms setting, so resistance can be measured. Set the volt meter on 200.
  
• 4 Take the black lead of the volt meter and touch the negative battery terminal wire. Take the red lead of volt meter and slide the tip into the terminal plug you just disconnected from the shift solenoid. Look at the reading you get on the digital display of your volt meter. Determine if the reading is between 12 and 25. Readings below 12 or above 25 tell you that the shift solenoid is not working. Reattach the plug to the shift solenoid and pull the second plug attached to the solenoid. Perform the same procedures on this plug wire. Replace the transmission shift solenoid after determining it is bad.
  

Gear Shift Indicator

• 1 Move the gear shift into the desired gear. Look at the gear labels and the arrow, or other indicator, to see if the gear shift indicator lines up with the selected gear.
  
• 2 Move the gear lever to another gear and look to see if the indicator lines up with the selected gear. Misalignment of the arrow will tell you if there is a problem. Moving the gear shift to "neutral" but having the indicator show the transmission is in "drive" tells you the gear shift indicator is not working properly.
  
• 3 Try each gear position to determine how much misalignment is in the indicator. Slide under the car and check for a loose gear shift cable. Check all the gear shift cable connections to ensure they are all tight and are not missing. Tighten any loose gear shift cable clamps or bolts. Replace the gear shift cable if you find that this is causing the misalignment with the gear shift indicator.
  

A common cause when the gear is on the steering column is a worn out pin. That pin holds the lever to the shift assembly. Try removing the gear shift lever and examine it.

• If the bushing between the pin and the shift is worn out, replace it.
• Examine the tip of the the gearshift and replace the shift if it's worn out.

Hope I've helped. If not please feel free to contact me with more details.

The mechanic should inspect then repair the shifting gears. And the gears on the transmission should be repaired or replace if worn out .the shift fork also have a problem it should be repaired or adjusted.

likely the shift rails are worn inside the trans. In changing shift, you have removed the wear on the end of the stick, but not the corresponding wear where the stick fits into. It will need to be taken apart to repair this. (would not hurt to have synchros replaced at the same time.) OR, replace transmission if you have an inexpensive one available.