From working on vehicles over the years I would check the linkage for wear problems. Check all your contact points where the rods contact the levers. Getting slack in the contact points can cause your shifter arms to not properly engage the transmission lever at the right point. Could be your forward contact points may be worn more than the recerse points as forward is most frequently used.
Other than that it may be an internal problem of gears or fluid flow. Tearng down an automatic or standard transmission I have never done.
I do not know if a vaccum problem would cause it or not.

Forward gears are gone.Replace transmission.

Thank you so much..oh woe are we..no money for that..YET!

You can go to a place like "Pull a Part" probably another name in your city but works the same- A big car junk yard. A car can be totaled from a bent frame or something and nothing wrong with the parts.

You can pull the transmission of an exact truck like yours. You check and see if they have your truck or another truck with the exact same part.

All models/parts cost the same. Run around 100 dollars for a tranny. At least you won't have to pay a lot for the part. And go find a cheap good mechanic that would put it on for a fraction of the cost. Those kind of mechanic are really out there. I found one in my city. Find the good mechanic before you pull the part.

You probably already know this but most car insurance companies will tow your car up to 10 miles for free or however miles it is to the dealership. Doesn't hurt to ask.