What gears

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chris3353

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idaho
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chris
Truck Year
1989
Truck Model
v2500
Engine Size
350
I have a 89 suburban 5.7tbi, 4L80 14 bolt and run 456 gears. I get ~12 mpg around town and ~15 on the highway. I cruise ~65.
 

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Blazerbiker

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Rifle CO
First Name
Stephen
Truck Year
1982
Truck Model
K5, actually a Jimmy since it's a GMC
Engine Size
504in
I've found 4.56s and 35s with the TBI350 to be a decent combo. Still very power limited but at that point it's mostly a power problem, not a gearing problem. I will say you should not be afraid of "over gearing" it. Your 30% overdrive will soak up a lot of gearing. If you're serious about 37-38" tires, at least 4.88s and maybe even 5.13s are the way. I'd do 5.13s. We've geared a couple GMT800 trucks with 6.0L/4L80 combos on 37s and 4.88 puts them at about stock rpm for a 2500 truck but you have a deeper overdrive and less power. Thus the 5.13 recommendation.
I hate to be the guy recommending smaller tires but with limited power, I'd consider keeping the tires smaller and like was mentioned earlier, maybe bail on the 14B front too. A GM D60 is a really solid system that seems to have gotten a bad rap somehow lately but they have always been able to take about anything you can dish out in a K5 on anything less than a 42. Keep in mind also that once you go past about a 37, your 241 quits being a rockstar and becomes something you need to think about.


Really hard use is not a slippery slope, it's a cliff edge you step over. Past 37s and you need strong axles, hydro assist, the tires themselves which are typically on beadlocks, power to move all of this with a trans that can take it, T-case strength and so on.

Moral of my story, put 5.13s in a GM D60 front and your 14FF rear, run 37s and go camping. Coilovers in front with our leaves in the back is a great system that will drive nice and have really good offroad capability too. And our coilover system works really well with a GM D60.
 

Red3833

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Location
Huntington Beach,Ca
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Frankie
Truck Year
1982
Truck Model
k20
Engine Size
383
5.13 are the way to go..
I have 700r4,205, 4” lift, 14b, 35” tires. cruises 75 no problem, one of the best upgrades I have done.
I like having option of going bigger tires,lift later on
 

Craig Nedrow

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Washington State
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Craig
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1973 (have two), 1985
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K10, K20, C20
Engine Size
350, 454, 6.2 Detroit
454, 4:10 205 14FF rear D44 front lockers in both. we have seep hills, truck does well here.
 

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