I have a 1992 4.3 5 speed I would like to put in a 5.3 keeping my 5 speed. Has anyone done this.

 

Would be quite difficult indeed. here is why:

-a 5.3 was not offered in 92
-The computers involved with the 5.3 will not be compatible
-Different Fuel injection system (EFI vs. TBI)
-6cylinder vs. 8cylinder
-Your 5spd is most likely not compatible (don't quote me on that one)
-engine mounts will defenitely be different.
-You will have to change gearing
-ETC ETC

As far as this kind of a swap goes, you would be better off trading for a truck like yours with a 350 or 305, or just leaving it as is. This kind of a swap would be a TON of work!