lock up solenoid? clogged valves?

[reezyfbaby07]

my 1995 f-250 7.3 has the E4OD tranny, and it shifts hard from 2-3, but all other gears shift fine, but i've also noticed that my overdrive doesnt kick in until about 36-38 mph, so when im in the city its constantly down shifting in that range, what is this the cause of? the truck has 350,000 on it and i plan on doing a trans flush this weekend but would rather wait if i have to fix the next problem....

also,

im told that my lock up solenoid is bad, heres what its doing:

at first it would stall when i put it in drive, then i put it in first and it drives, and then i shift up to 2nd then overdrive, it did this for about a day. I ran sea foam trans tune thru it and it was fine, then the next night it did it again for about 3 minutes after i put TVF (trans valve fix) in, but since then its ran fine, is my valve clogged with gunk and varnish? or is it my lock up solenoid? i would rather wait to do the trans flush if i have to replace the solenoid, but if its gonna help it, i would rather do it asap.

PLEASE HELP!!!