I have a 1994 chevy s10 Tahoe 4 by 4 with only the 2 buttons 4hi 4low why don't it have 2 wheel drive button

look on the dash for a 4wd button or switch. may be located between the steering wheel and the radio. when you turn the knob to select 4hi, 4lo, 2hi, or auto, the indicator light above the corresponding selection will flash until the shift has completed. if the light stays flashing there is a fault in the 4wd system

the residual force makes it look like its working on a lift ,
check your wheel sensors the speed sensor determines how fast each wheel is turning say in the snow , if the sensor fails it wont go into 4 wheel drive.

There should be a button on the dash. Push either 4hi or 4 low to activate the four wheel drive.

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Have you had codes checked ? While connected to a good scanner that will check transfer case switch to show if switch is working, and it could be the switch on the side of the transmission.

On any suv with 2 and 4 wheel drive options 4 low generally means that the transmission is in 4 wheel drive low gearing option so that the most possible torque is transferred to the wheels by way of what would be called a granny gear. What you will need to do is check your 4 wheel drive settings to see if the transmission has been put into this option which is either on a separate shift lever or a push button either on the shift handle or on the dash. Your owners manual should also direct you to where the selector is at.

First try disconnecting the battery for about 10 minutes. This will reset all of your electrical systems and perhaps fix the issue.
If this doesn't work then check the 4 wheel drive transfer case electronic module in the right kick panel on the passenger side for corrosoion. If any posts are broken are burnt they will need to be replaced.

Hwy driving 2hi, mud driving 4low or auto 4wd.

check that the actuator motor on the transfer case works properly.The motor could have a dead spot like a starter motor.

try seeing if the cable going to the front differental is pulling in to engage the front axle?

try changing the vacum switch on the trafer case