I have a 2004 Ranger with a 5 speed manual, and if I try to shift into 2nd too fast, it just won't go, it is like something is blocking the shifter. Any ideas as to why?

 

Welcome to the forum

Look at this video first: www.youtube.com/watch?v=wCu9W9xNwtI

In your transmission there are 3 Shift Rails, 1/2, 3/4, 5/reverse
Each shift rail has 1 Shift Fork attached
The 1/2 shift rail moves it's shift fork to engage 1st or 2nd
The same for 3/4 and 5/reverse

Each shift rail must be moved back to "Neutral" position before you can move the shift arm over to engage another shift rail.

Each shift fork is holding/on a "dog gear" that is attached to Output shaft
The "gears" in the transmission are attached to the Input shaft

When you push the shift arm in to 1st, the 1/2 shift fork pushes the dog gear towards 1st gear, there is a softer metal synchro "gear" that matches the spin of the dog gear to the spin of 1st gear, once spin is matched tabs on dog gear slide into slots on 1st gear, 1st is now engaged.
Matching the spin is the hard part

When stopped the output shaft(driveshaft and wheels) are at 0 RPM
1st gear is at Engine RPM, 700rpm idle.
You push in the clutch, which disconnects engine RPMs from Input shaft, and that allows 1st gear to slow down to 0 RPMs, so dog gear can engage 1st gear.
If 1st is hard to engage when stopped then clutch disc could be rubbing on flywheel, so synchro is having a hard time slowing 1st down to 0 RPMs, slave may have some air in it so isn't disengaging clutch disc enough.

2nd gear, when you pull back on shift arm to go from 1st to 2nd gear the dog gear slides away from 1st and towards 2nd gear, getting to 2nd synchro and then trying to match the spin, output shaft to input shaft.
You could have a problem on the shaft itself, dog gear isn't sliding well on it.
How does it shift with engine off?

Could be synchro failing, not allowing dog gear tabs to line up with 2nd slots.

If it does shift to 2nd but just not fast then synchro may not be working to match spins, you have to wait until dog gear and 2nd match up

When stopped how well does it shift into 2nd gear?

 

With engine off, no issue.

 

Then dog gear is not binding on the shaft, and 1/2 shift fork and shift rail would be OK if no binding with engine off.

You have an M5OD-R1HD transmission, they have a very good track record since first used in 1988/89.

One thing people do say is that the Mercon ATF(yes automatic transmission fluid) specified for these transmissions can cause harder shifting in some.
Switching to a synthetic ATF has gained smoother shifting for some.
I have not tried it, but those that had shifting issues swear by it, so............

You could have a problem that will get worst over time, and trans will have to be pulled and rebuilt, but trying a different trans fluid may fix the problem permanently or temporarily, or may make no difference at all.
Your call.

Google: M5OD-R1 best fluid

The HD is not needed at the end, that just means the transmission had 1 extra bolt hole on the bellhousing to fit the 4.0l SOHC engine, transmission itself the the same since 1988/89

There is nothing external on these transmissions that can be "out of adjustment", so problem is internal, and clutch issue would be present shifting into 1st when stopped

What about engine running but vehicle stopped, how does it shift?
Let out clutch in Neutral, engine idling, that starts "gears" spinning at 700 RPM, then push in clutch and try shifting to 2nd gear

 

I have been having the same issue with my 2010 Ranger. Replaced the clutch, flywheel, pilot bearing, slave and master cylinder, throw out bearing, and performed extensive bleeding of the system; still have the same problem. I have performed a few tests to isolate the issue, and eliminated the clutch/hydrolic system by lifting the rear axle and engaging/dis-engaging the clutch in each gear; wheels do not spin when clutch is engaged. With that confirmed and the fact the transmission shifts wonderfully when the engine is off, I believe that the issue is internal. Syncro teeth are most likely fine due to no grinding, and shift forks/rails most likely fine due to easy shifting when engine is off. This leads me to think the strut key groves are worn within the syncro and/or the collar that is allowing the syncro to lash(move) to the point the teeth on the syncro and collar are point to point and blocking the shift from happening. I cannot confirm this is the issue until I pull the trans and tear it down, which isn't going to happen for some time, but hopefully this will give a starting point for others that are having similar transmission behavior as myself.

 

I see this thread is very old I have a 2010 ranger with exactly same symptoms. I've replaced the clutch and everything around it.
Did anyone find the issue?