The K2XX Silverado has no transmission dipstick, which throws most people off. You drain through a plug in the pan, refill through a plug on the side of the case with a pump, then set the level by letting excess run out of that same port with the engine idling and the fluid at roughly 100 F. One drain only gets about half the fluid out, so many owners do two services a few thousand miles apart.
The thing people get wrong is fluid type. 6L80 trucks take DEXRON-VI; 8L90 trucks (2015+ 6.2L, later 5.3L) take DEXRON-HP, and putting VI in an 8L90 is a well-documented cause of low-speed shudder. The second mistake is draining before checking that the fill plug will actually come loose - crack the fill plug open first, every time.
| Item | Type | |
|---|---|---|
| Floor jack 2-ton minimum, or drive-on ramps Lift the truck to reach the pan and fill plug; truck must sit level for the level check. | Required | shop |
| Jack stands 3-ton pair, all four corners preferred Support the truck safely and keep it level while fluid drains and is checked. | Safety | shop |
| Drain pan 10+ quart capacity, wide Catch the 5-7 quarts that come out of the transmission pan. | Required | shop |
| Hex bit socket set Metric 5-17 mm hex bits, 3/8 in and 1/2 in drive Pan drain plug and case fill/level plug are internal-hex; 8 mm hex is typical for the drain, the fill plug is a larger hex. | Required | shop |
| Ratchet and extensions 3/8 in drive ratchet, 6 in and 10 in extensions Reach the fill plug on the side of the case past the crossmember and exhaust. | Required | shop |
| Breaker bar 1/2 in drive, 18-24 in Fill plugs are often very tight and the hex will round if you slip. | Recommended | shop |
| Fluid transfer pump Hand or drill-driven pump with flexible hose, ATF-compatible Only way to push new fluid uphill into the side fill port; there is no dipstick tube. | Required | shop |
| Scan tool Reads GM transmission fluid temperature PID Level is only valid at roughly 95-115 F (35-45 C) fluid temp. | Required | shop |
| Infrared thermometer -20 to 500 F Backup temperature check on the pan if your scan tool will not show the PID. | Recommended | shop |
| Torque wrench 3/8 in drive, 10-80 ft-lb Set the drain and fill plugs to spec; the case is aluminum and strips easily. | Required | shop |
| Shop rags and brake cleaner Clean the plug areas before opening so nothing falls into the pan. | Consumables | shop |
| Transmission fluid 6L80: DEXRON-VI, ~6 qt. 8L90: DEXRON-HP (Mobil 1 Synthetic LV ATF HP), ~7 qt Refill; buy one extra quart so you can overfill and let it settle out to level. | Parts | shop |
| Drain and fill plug seals Plug washer/O-ring per plug, GM part Both plugs use a seal that should be replaced to avoid weeping. | Parts | shop |
| Nitrile gloves and safety glasses Hot ATF runs down your arm when the plug comes out. | Safety | shop |
The 4.3L V6 and most 5.3L trucks use the 6L80 six-speed with DEXRON-VI. The 6.2L L86 (and 5.3L on later builds) uses the 8L90 eight-speed, which requires DEXRON-HP fluid and has a slightly larger drain-and-fill capacity. Plug hex sizes are similar between the two, but the fill plug location on the 8L90 sits a bit higher on the case and is harder to reach past the crossmember.
| Transmission pan drain plug (6L80/8L90) | verify in the service manual (commonly around 15-20 ft-lb / 20-27 Nm) |
| Case fill/level plug | verify in the service manual |
| Transmission pan bolts (if pan is dropped) | 97 in-lb (11 Nm) typical for 6L80 - verify in the service manual |
Plug locations and the temperature-based level procedure are correct for these transmissions, but the exact hex sizes and plug torque values vary by transmission and build date, so confirm your drain/fill plug sizes and torque figures against the GM service information for your VIN.
Expect about 5-6 quarts on a 6L80 and 6-7 quarts on an 8L90. Total system capacity is roughly 11-13 quarts, so a single drain replaces about half.
It is an internal-hex plug on the side of the transmission case, above the pan rail, reached from under the truck. Loosen it before you drain anything.
Practically, yes. There is no dipstick, and the level is only correct when the fluid is around 95-115 F, which you confirm with a scan tool reading the trans fluid temp PID or, less accurately, an IR thermometer on the pan.
No. The 8L90 requires DEXRON-HP (Mobil 1 Synthetic LV ATF HP). GM issued service bulletins replacing the original fluid with HP specifically to cure torque converter shudder.