Depending on what you use your truck for you could either use the VQ40DE out of the Frontier/Pathfinder/Xterra (261 hp/ 281 tq) or a VQ35DE out of a Z (287 hp/ 274 tq).
There's a huge list of variants on the VQ design but the two I listed are the most likely candiates for a swap for a few reasons: they''re not from rare or limited edition cars so they're both inexpensive and plentiful, they've been around for a while so parts are in circulation and they're well supported online in case you need help with torubleshooting or want to do some aftermarket modification (which you'll be doing from the beginning with your swap into a Chevy!).
As far as mileage, i get anywhere between 25-28 mpg in my Z (almost all highway miles) and 19-21 miles in my Xterra (lots of stop & go, and it's heavy!). You should get better mileage than the Xterra (because of the S10's lighter weight) but might not get as good as the Z (because of the Z's better aerodynamics). Here's a link to all the factory service manuals on NICO
The VQ40 was used in: 2005 - current Frontier
, 2005 – current Xterra
, 2005 – current Pathfinder
. The VQ35 was used in the 2002-2005 350Z
(except for the Track & 35th Anniversary models in 2005).
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