4L60E slipping in 2nd — keep rebuilding the 60E or swap to a 4L80E?

We don't have a source that diagnoses a 2nd-gear slip specifically, so have it checked before deciding. For comparison, a sun shell failure makes it lose 2nd, 4th and reverse entirely rather than slip.

The rebuild-or-swap decision: a built 4L60E handles about 450–500 hp on the street if the rebuild covers the known weak points and heat:

The upgrades that matter (Speedway):

• 3–4 clutch pack: stronger frictions and steels — one of the most common failure points.
• Hardened input shaft: keeps it from twisting or breaking with hard launches or sticky tires.
• Sun shell: a beefed-up shell.
• Valve body / shift kit: firmer shifts cut clutch slip and heat.
• Torque converter: stall matched to the cam and powerband; for high torque, one with an anti-ballooning plate.
• A large external cooler: heat is what kills these.
• Tuning: shift timing and line pressure calibrated for the build.

If the truck is heavy, tows, or makes more power than that, the 4L80E (440 lb-ft stock) is the durable answer. What a 4L80E swap takes: a flexplate with the 11.5 in converter pattern (the 4L60E's is 11.062 in), a computer that runs it (the factory PCM it came with, or a Holley Terminator X Max, which has 4L60/4L80 control built in), and a crossmember and driveshaft to suit — the 4L80E is heavier and longer than a 4L60E.