I keeper replacing my fan blower switch on my 99 chevy tahoe

Based on the detailed information you've provided, it seems that you've done a thorough job of testing the major components related to the blower motor system in your 1999 Chevy Tahoe.
Here are a few possibilities and additional steps to consider:

High Resistance in the Circuit: Even though the wiring and connectors appear to be in good condition, there might be high resistance somewhere in the circuit that only becomes significant under load. This could be due to a partially broken wire, a corroded connector, or a faulty switch. Carefully inspect the wiring harness for any signs of damage, wear, or heat exposure.

Issue with the Control Switch or HVAC Control Unit: The problem might be with the control switch or the HVAC control unit in the dashboard. These components can sometimes develop internal faults that are not immediately apparent. Consider testing the switch and control unit if possible.

Ground Connection Problem: A poor ground connection can cause voltage drop issues. Make sure the ground connections related to the blower motor circuit are clean, tight, and free of corrosion. This includes not just the ground for the blower motor, but any related grounds in the HVAC system.

Voltage Drop Test: Perform a voltage drop test on the blower motor circuit. This test is done by measuring the voltage across different parts of the circuit while the circuit is under load. A significant voltage drop across any specific part of the circuit would indicate where the resistance problem lies.

Check for Overloading or Short Circuits: There could be an issue elsewhere in the electrical system that's causing an overload or short circuit when the blower motor is connected. This might be difficult to diagnose without specialized equipment.

the blower switch in dash needs replaced. I assume it has 4speeds, and the other 3 work, just not the highest. if this is correct, then it is the blower switch (dial)

take a look at the connector that feeds the resister that mounts next to the fan under the dash below the glove box the connectors over heat and become loose making the connection fail

problem in your blower switch

THE FAN SWITCH PROBABLY NEEDS TO BE REPLACED. IT MAY HAVE BURNED UP CONTACTS.

Sounds like the control which is yep a resistor

I just took my 04 Tahoe in for the same thing and it was the a/c actuator.

Look at the connector at the blower resistor. They melt. Bottom of right side of dash under the black close out panel. GM sells a repair kit for this.

check fuses & power to blower fan motor,plug connections.then apply 12 volts to blower fan motor if it dont turn its bad

It doesn't blow cold air? Doesn't come on at all? What's the problem? If it doesn't blow cold after a charge, it leaks. Either on the compressor or in a line or both. To start at the dealer, a compressor is about $1200. That's what they told me. I have two leaks. You can buy remanufactured compressor on ebay for under $200. Or find a good shop (polar bear around here) with reasonable prices and have them do it for something in between.

If it no air is moved at all by your climate control system, the blower motor could be fried, the switch may have gone bad or a fuse is blown perhaps. If it moves air, but not cold air, recharge it and see if it stays cold. If so, great! If not, find the leak.