I have a 1996 Silverado K1500. A few weeks ago I decided to see how long it would take for the thermal actuator to engage the front differential. The result: 51 seconds. 51 seconds?!? It was 88 degrees outside for #%/@'s sake! I had enough and decided to order this Dorman 600-101 along with the Dorman 600-600 Actuator Wire Harness. Amazon had the best price I could find and I know they have excellent customer service in case there's a problem. I received both items yesterday and performed the installation. (Note: The wire harness kit also includes a spacer that needs to be inserted into the differential before installing the actuator.) The actuator comes with sealant/thread lock already applied to the threads so all I had to do was screw it into the differential housing. (Note: 1-3/4" wrench needed).
WOW; what a difference! Now my front axle engages in a couple of seconds. Not only that, but it stays engaged even when I switch off the engine. I'm definitely looking forward to no longer having to wait so long for my 4X4 to engage. I almost got into an accident once when my truck started sliding backwards down an icy hill -- and into oncoming traffic -- while I was waiting for the 4X4 to engage! Luckily the POS thermal actuator finally kicked in before I hit anybody, but I always had to plan well ahead after that incident.
The only potential problem I can see with the Dorman 600-101 actuator is that it is made of nylon instead of metal (like the old thermal actuator). It is my understanding that the GM actuators are made with nylon as well, so maybe it won't be an issue. (Time will tell.) Peace.