travmanzz
not sure what they put into your truck but if you are thinking of changing gears you might find this chart to be helpful. copy and paste the following into a word doc it may give you some thoughts about gear ratios and tire sizes. you can find this and more at
http://www.offroaders.com/tech/gear-ratio-chart.htm.
About this Engine RPM / Tire Size chart:
The following chart of Tire sizes and axle gear ratios are meant to give a general idea of the relationship between the differential gear ratio and the tire size and what effect the ratio has on power output and fuel economy. The chart is based on RPM levels at 65 mph (105 kph) and a drive train running at a 1:1 gearing ratio, meaning the transmission and transfercase are passing power straight through at a one to one ratio without reducing or overdriving the engines rotations per minute before it reaches the differential. It is also worth noting that a manual transmission will be the most efficient at transferring power through to the axles and that an automatic transmission will have some inherent slippage without a locking torque converter. Also with an overdrive transmission, your engine RPM will be approximately 20 to 30% less than shown here depending on the overdrive ratio.
Good Fuel Economy but less power, good for flat highway driving
Best Overall Performance, good for daily driving
Highest for Power and Towing but reduced fuel economy, higher engine RPM
Tire
Size DIFFERENTIAL GEAR RATIO
2.35 2.73 2.94 3.07 3.21 3.31 3.42 3.55 3.73 3.91 4.11 4.27 4.56 4.88 5.13 5.29 5.38 5.71
28 1833 2129 2293 2395 2504 2582 2668 2769 2909 3050 3206 3331 3557 3806 4001 4126 4196 4454
29 1770 2056 2214 2312 2417 2493 2576 2674 2809 2945 3095 3216 3434 3675 3863 3984 4052 4300
30 1711 1987 2140 2235 2337 2410 2490 2584 2715 2846 2992 3109 3320 3553 3735 3851 3917 4157
31 1656 1923 2071 2163 2261 2332 2409 2501 2628 2755 2896 3008 3213 3438 3614 3727 3790 4023
32 1604 1863 2007 2095 2191 2259 2334 2423 2546 2669 2805 2914 3112 3331 3501 3610 3672 3897
33 1555 1807 1946 2032 2124 2191 2263 2349 2469 2588 2720 2826 3018 3230 3395 3501 3561 3779
34 1510 1754 1889 1972 2062 2126 2197 2280 2396 2512 2640 2743 2929 3135 3295 3398 3456 3668
35 1466 1704 1835 1916 2003 2065 2134 2215 2328 2440 2565 2664 2845 3045 3201 3301 3357 3563
36 1426 1656 1784 1862 1947 2008 2075 2154 2263 2372 2493 2590 2766 2961 3112 3209 3264 3464
37 1387 1611 1735 1812 1895 1954 2019 2095 2202 2308 2426 2520 2692 2881 3028 3123 3176 3370
38 1351 1569 1690 1764 1845 1902 1966 2040 2144 2247 2362 2454 2621 2805 2948 3040 3092 3282
39 1316 1529 1646 1719 1798 1854 1915 1988 2089 2190 2302 2391 2554 2733 2873 2962 3013 3198
40 1283 1491 1605 1676 1753 1807 1867 1938 2037 2135 2244 2331 2490 2664 2801 2888 2937 3118
41 1252 1454 1566 1635 1710 1763 1822 1891 1987 2083 2189 2275 2492 2599 2733 2818 2866 3042
42 1222 1420 1529 1596 1669 1721 1778 1846 1940 2033 2137 2220 2371 2538 2668 2751 2798 2969
43 1194 1387 1493 1559 1630 1681 1737 1803 1894 1986 2087 2169 2316 2479 2606 2687 2733 2900
44 1166 1355 1459 1524 1593 1643 1698 1762 1851 1941 2040 2119 2263 2422 2545 2626 2670 2834