Tach cutting in and out

[1993 F200]

Hello I am new to this forum and I have a 1993 idi NA that I have swapped over to 1/2 ton running gear and have lowered 6” it is having issues with the tach cutting in and out and it is not consistent when it cuts in and out besides it seems to happen after the truck is warmed up. I have had the gauge cluster rebuilt, TPS replaced, Cam sensor replaced wires at plug on harness look good, speed sensor on rear pumpkin replaced and I am at a loss now.
Any advice would be welcomed.

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[Clb]

Check the wires on the tach sensor wires on the timing chest by the filler...

 

[DirtyWood]

Is the signal cutting out and causing shifting problems with the E4OD?

 

[1993 F200]

I have checked the wires and replaced the tach sensor the wires from the harness look good.
Yes whenever the Tach cuts out and it will bounce up and down the trans freaks out and doesn’t know what gear to be in so it will start shifting up and down

 

[DirtyWood]

When the tach goes wonky do any other gauges fluctuate?

 

[1993 F200]

No all other gauges are acting fine

 

[Black dawg]

From what I remember, the tach goes to the ecm before it goes to the cluster. If the computer is in the stock location, water runs down, and if the connector isnt tight or sealed , water can get in. Also check the relay for the computer.

 

[1993 F200]

I replaced the TCM already also sorry I forgot to mention that in the original post it was about five years ago now but the truck has only been driven maybe 5,000 miles in that time the connection appears to be tight on the firewall.
That is the only computer I know of on this truck.