Hello my truck has been working pretty hard last few days and today I had an issue. Thankfully after I dumped a load of rock and on my way home I got stuck in 5th/6th gear when pulling out on the highway and going up a hill so was shifting kinda fast and once I peaked the hill I couldn't upshift and had to drive home at 20ish mph a good 15 miles. Wow was that frustrating. And I was trying my damndest to get it out of gear the entire slow ride home. Any pointers on how to unjam it? And everything I found online about fixing what caused it requires it to be in partial reverse to disconnect upper cap. How do I get past this snag?

Thanks mike