TBH, the first thing I thought of when I saw this, was 'sunshell'.
For the OP... usually when this goes, you'll hear a fairly loud noise when it happens (because metal parts have sheared off / apart). If you were at highway speed, which it sounds like you were, perhaps you didn't hear anything. But when it goes, it takes out all the gears, because the front and rear planetary assemblies reside in that component (that's why it's called a 'sun' shell - the sun gear of the trans lives in that area, along with the smaller planetary gears)
Anyway... if it is the sunshell, it's a full rebuild (or replacement). To rebuild, the trans has to come out, be fully taken apart (the sunshell lives at the back of the case), damage assessed, new parts put in. There are aftermarket shells which are hardened and won't shear, like the factory one may have done with yours. You'll also want to replace normal wear parts, like the clutch packs and band, and a corrective shift kit (replaces other wear parts in the valve body). Finally, adding an auxiliary trans fluid cooler will supply maximum insurance against overheating, especially if you live in a hot summer climate or you do any towing.
The cheapest option is to source one from a junkyard and swap it in, as-is. That might run anywhere from $250-$800 or so, depending on source / condition, and if you do it yourself / get a buddy. A shop will charge labor, plus markup on the trans, for sourcing it for you. If you can afford it, put in a new torque converter (stock equivalents run about $200). The reason for that is 'cheap insurance', since a used one can have burnt internals, or metal 'trash' in it that will spread around to the rest of the trans & potentially destroy it. And if rebuilding, always put in a new converter.
If you get to pick the vehicle your junkyard trans comes out of, look for one with collision damage (the thought being that it was running when the vehicle met its end.) A vehicle with no body damage is probably there because something expensive in the driveline broke, and the owner judged that it wasn't worth the spend to fix it.
Biggest downside with this option, of course, is that you have little (if any) warranty. Might last as long as the rest of your truck; might fail in a week. Crapshoot.
Rebuilding a trans is not for a novice (and requires some specialized tools), so you'll need someone to do the rebuild, if you go that route.
A rebuild will run anywhere from $1800-up, depending on how many / what parts get replaced, and who does the work. (the hardened sunshell runs about $150-200 or so). That will include labor, which should be quoted as a flat-rate job. Mine ran $1900, but that was a few years back, and I got a good rate from an independent shop I trusted. Plan for $2000-2500 or so. Try to avoid the franchise shops like Aamco and similar, if you have a choice -- you'll pay more, and just get a 'factory equivalent', WRT parts used. Not to mention that the skills of their techs can vary widely, to put it nicely, provided they rebuild it in-house.
The advantage with rebuild, is that you'll get some sort of warranty with it (I got 2yrs with mine).
If done correctly, addressing the few known issues of the 4L60e, it'll outlast the rest of the truck (as long as you keep the fluid / filter changed every 50,000 miles, minimum).
A third option is to get a reman shipped from a company (Monster Transmissions is one company, to get you started, although I've not heard good things about them, lately). These come via freight, and you either pick up the trans at a local trucking yard, or they'll provide liftgate service to your curb / garage (built into the delivery charge). Then you have someone install it (and these places will usually insist on you using an 'approved' installer from a list they provide, or you forgo warranty). While these places will use the better parts, you can imagine that this is the most expensive option, all-in. Prices will probably start at $3000 / up, and may not include installation fees.
The 4L80e is considered a very good trans (even though GM built them cheaper & less reliably as time went on), especially compared to similar transmissions from F**d and Chrysler from the same time period. It's worth the spend, if you want to fix it, and especially if you put in the 'good' parts, if rebuilding it. You have 153K on the engine; if you keep up with the oil changes, replace a few items as they wear, etc., you can get another 100K miles out of the truck. Rust is a factor, if you live where they use salt on the roads in winter. Since these sit a bit lower to the ground than even a 1/2 ton pickup, the frame areas rust easier. Body panels can be repaired / replaced. A frame rusting out is usually 'the end'.
Our fingers are crossed that you won't need a full rebuild / replacement. But I'd get my mind set that it probably will be needed, if I were you.
