4.3 in 71 getting 19 MPG?!?!?

[iluvmy72]

OK....my friend put in a 1989 4.3 with a stock throttle body into his 71 LWB truck and he says he's now getting over 19 MPG on the HWY. Is he lying?! He said he also has great power. He also bolted over the 700r4 tranny as well. The engine is stock except for the headers. Has anyone else done this and has had good luck with gas milage? I'm thinking of putting in my 4.3 engine from my 88 astro into the truck. The engine and tranny were rebuilt just 3 years ago.