Torque Converter
Your 4x4 isn't going anywhere without a torque converter between its engine, flywheel, and automatic transmission.
Exacting design and placement of vanes and blades in a converter's turbine, all lubricated by the transmission's fluid, combine to double engine torque. Engine rpm in and rpm out to the transmission are unchanged. The stator "floats" between the turbine and impeller.
A typical fullsize truck torque converter-a 12-inch-diameter, 6-inch-thick, 33-pound lubricated component-utilizes precisely vaned and bladed impellers, stators, and thrust turbines (plus a little magic) to double the torque produced by your engine's driveshaft.
For optimum performance for your trail driving, your engine, torque converter, and transmission need to form a coordinated team. Your transmission tech, probably after talking with technical advisers at a transmission overhauler and torque-converter manufacturer, can make the match.
There are a range of torque-converter modifications, to include various stall speeds, to match your engine/transmission combo. For demanding off-pavement use, Don Randolph of torque-converter builder Daaco in Cookesville, Tennessee, can provide your transmission shop with a converter that is "indestructible."Torque converters can have weaknesses that can sometimes result in catastrophic failure, "killing" the converter. In our case, our torque converter's turbine and stator race showed signs of cracking when they were removed. Fortunately, these cracks were found at converter overhaul-before failure.
Preventions
As has been said before, heat is a destroyer of transmissions. To increase the tranny's reliability and lifespan, keep it cool.
An operating temperature of 175 degrees Fahrenheit is considered nondetrimental to your transmission fluid. Operating temperatures above that will damage fluid and harden seals, causing internal leaks that shorten the life of your tranny. According to technicians at Lubegard International:
The OE 1st-2nd gear accumulator spring (left) was replaced by a heavy-duty "never fail" spring during overhaul. | 
Cracks in the impeller center (only one of the three shown) would likely lead to catastrophic failure, possibly threatening the transmission. | 
A cracked stator race, with its roller bearings, can suddenly fail and scatter loose bearings through the converter. |
Internal temps of 200 to 240 degrees cause oxidation and thickening of fluid; at 240 to 250, varnish begins to form and additives are cooked out; and from 260 to 300, fluid degrades to the point where clutches slip, being virtually unable to move your truck.
Your tranny's multi-channel valve body contains a number of ball bearing-like valves that need to move freely at various shift points. Thickened transmission fluid can deprive your radiator, and its closely mounted OE transmission-fluid cooler, of airflow they need.
An electronic transmission valve body is distinguished by the two copper coils at left; a non-electronic transmission's valve body has no copper coils.
An auxiliary transmission cooler such as NAPA's Ultra-Cool (PN 4822) mounted on the front of our Tahoe's radiator has lowered our tranny's operating temperature by 50 degrees. Cooler cost was $49.99, plus one-hour installation.
TransGo offers two transmission reprogramming kits, one for vehicles under 5,000 pounds, and one for vehicles over 5,000 pounds, which TransGo says can "increase gas mileage and easily double the life of a transmission."
Beyond the above, check your transmission fluid whenever you check your engine oil, making sure to follow your owner's manual for fluid level check and addition of fluid.
Finally, your transmission filter should be checked and fresh fluid added about every 50,000 miles or as per the manufacturer's recommendations.
Adding it Up
So what did it cost us? And what would we have paid to have a dealer do the work? A Chevy dealer bid for a "transmission overhauled for General Motors" was $2,624 installed with a rebuilt torque converter; the work was warrantied for 100,000 miles or 36 months, whichever comes first.
By contrast, our Odessa rebuild totaled $1,577 installed, with rebuilt torque converter, warrantied for 6,000 miles or six months. We're way beyond those figures already.