Sdillard

Hello all F150 owners
I joined this forum in hopes of gaining knowledge from experienced Ford owners
I have a slight situation with my current F150 with the speedo acting weird in which I will explain, but first let me tell you about my Ford I own. It is a 2008 F150 4.6L 4x4 super crew with 152,000 miles
My issue is with my speedo/transmission issue
If I drive my truck to work which is appr. 31 each way - going to work no problem ,coming home is when it acts up if I am driving down the road ( always starts doing the problem when going down a hill about 5 miles from home ) if I let off the gas and gain speed the speedo will almost loose the connection in a sort But as soon as I you h the gas pedal - not pushing it down the speedo will work correctly?
Some history on this , didn't do this issue until the wonderful manufacturing flaw of the intake manifold started leaking, replaced coil packs twice spark plugs twice, obviously intake replaced speed sensors both on tranny ,turbine sensor and speed sensor
Pre intake and speed sensors the truck would run great cold and after about 20-30 miles the speedo would jump from 50-60mph down to zero back to another speed up to the 50-60mph mark and if I called to a stop after the speedometer did its thing it would almost "slip" the transmission it would continue to do this until I put truck in reverse?
The slip would be every stop and almost as if it was stuck in second gear until eventually it would downshift itself after around 30ft after that it would shift all gears like it should?
Now after replacing the manifold and sensors it's been 27 days and the speedo is starting to act up again .... No slipping just yet but who knows
Also just so you know no codes come up and transmission fluid is not burnt or smells burnt?
This is very confusing to me as I do all my work on truck myself not ase certified just watched my dad very closely who is a very certified mechanic for 40 + years
Any help with this would be great
Thanks