Guys I did a search (google and on here), it's supposed to be (as you stand facing the engine from the front) on the back rear of the block.

But I can't find the darned thing!

Pics would be appreciated

 

Regarding the 4.2L engine, the manifold pressure sensor is mounted on the intake manifold (not block). You can see the wiring harness connector for the sensor, by looking at the rear of the engine above the torque converter bell housing.

Page 1331 of the 2006-2008 repair manual has an illustration of the sensor and the associated wiring harness connector and page 1336 shows a closeup drawing of the sensor housing and seven bolts that attach the housing to the rear of the intake manifold.

Regarding the 5L engine, the repair manual has an illustration 12 on page 1033. I believe that is the manifold pressure sensor, however that manual assumes you know what you are looking at and captions are not provided.