1998 Chevrolet Silverado • V8 4WD Automatic • 150,000 miles

What would cause a 1/2 ton 98 extended cab Chevy silverado, 4 wheel drive truck start shifting slow into first gear, but work fine from that time. Also the speed ometer quit working along with the RPM gague. It doesn't shift as soon as you put it into drive, but have to rev up the engine some, then it is fine.
March 2, 2011.

Have the vehicle speed sensor checked.