I Bought a 06 Toyota Tacoma Prerunner a couple a years ago (about 260,000 miles then), and it seems to have 2 distinct transmission problems;

The first one is, when setting off I can feel the transmission jump or slip, this does not happen every time, only about 50% of the time. It also sometimes occurs when sitting still at a red light, I'll be completely stopped for about 10 seconds, and then the same thing will happen. This occurs rarely, maybe 5% percent of the time. (With what little I know about transmissions, it seems to me to be the torque converter, but that's just my uneducated opinion.)

The other problem is a little harder to explain, so feel free to ask to more details.

When driving I shift into D, as you do in an automatic, but when I hit 30-ish (I think in-between 2nd and 3rd or 3rd and 4th, I don't remember) it feels and sounds like I'm hitting the dummy bumps on the side of the road. This happens at the same speed when slowing down, this occurs almost every time. I tried to do some research on my own about this, hoping it was a cheaper fix I didn't find much information regrading this. But what I have done for the past year and half is I drive in "4" (directly to the left of "D"[ Overdrive not possible]) and the dummy bump thing never occurs, then  I just shift back over into "D" at high speeds, (So that It shifts up into overdrive) and back into "4" at low speeds, kinda like a 2 speed manual.

A short backstory of when we bought the truck; I'm 18, bought the truck 2 and half years ago, and my mom and I had been looking at trucks for months, (I live in the south, so a truck opens the door to more side jobs) then one day this truck show up for sale on the side of the road 30 seconds from our house. I had to go out of town the week we were going to look at the truck, so my mom and our mechanic friend went, and the between the two of them they decided to buy it. The only thing they saw out of place was: there was, and still is, a pink bushing/ spacer of the radiator fan. This bushing is not from the dealership because we asked, and the man took the truck to the dealer for any and all services, he even spent 60 dollars to get a lightbulb installed, we have the all the receipts to the truck (that we know of). The man do not even know how to open the hood, true story. We also can see from the receipts; 6 months before he sold the truck, he took it to the dealer to look at the transmission, and they recommended a new transmission. We asked again anyway and that still holds up.

Hope I did good job explaining these two problems.

Thank you,

Isaiah

Notes/ Questions:

It is a closed system, mounted to a V6

The dealership and small transmission shops want 5,000 to replace the transmission, which is not an opinion for an 18 year old

The previous owner bought the truck new.

The previous owner worked at a casino, so I don't think he did any towing 

Are these two problems related?

Is the only solution to just replace the transmission?

Do I keep doing what I have been till it gives out?

Where did the pink spacer come from?